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The heart is the main part of the circulatory system of your body. The heart and the circulatory system makeup the cardiovascular system. The major job is to pump blood, which then nourishes and oxygenates the entire body.

It is an important organ; a healthy heart provides your body with the right amount of blood it needs to function well. When illness or injury weakens your heart, your body’s organs do not receive enough blood to function normally.

What is a heart? 

The heart is a muscular pumping organ that works continuously to send oxygenated blood to all the parts of your body. It is slightly larger than a clenched fist and is well protected by the rib cage.  Your heart acts as a pump that pushes blood to your body’s organs, tissues and cells. Blood delivers oxygen and nutrients to each cell and removes carbon dioxide and waste products produced by the cells. Blood travels from your heart to the rest of your body through a complex network of arteries, arterioles and capillaries.

Most part of your heart is made up of muscle (cardiac muscle) that works continuously throughout the body. It beats on average 100,000 times a day. During this time, it pumps over 2,000 gallons (7571 litres) of blood through the body.

Your heart is located in front of the chest, in the protective thoraxic cavity behind the sternum and coastal cartilage and rests on the upper surface of the diaphragm. It is present in between the two lungs of your body which occupy the lateral space called plural cavities angled to the left. It is present slightly left to your sternum (breastbone), your left lung is smaller

Everyone’s heart is a slightly different size. In general, adult hearts are about the size of two clenched fist, and children’s hearts are about the size of one clenched fist.

The size of your heart is roughly the size of your fist. The dimensions of the heart are 12 cm in

length, 8.5 cm in breadth, and 6 cm in thickness

Your heart weighs between 200-425 grams. The size of the heart varies in male and female, the average weight of the heart is 230-280 g for women and 280-340 g for men.

Understand the parts of your heart

Layers of the Heart

What is pericardium?

Your entire heart is enclosed by a double layered structure called pericardium. In between the two layers is a cavity called pericardial cavity.  This cavity contains a pericardial fluid, which lubricates the heart, permits it to contract with minimal friction and protects the heart from external injury.

The main function of pericardium is to control the movement of the heart. It protects your heart from infection, lubricates it and prevents excessive expansion in acute volume overload.

The various components of the heart are encased in a thin layer of tissue called the pericardium.

Improper functioning of pericardium can result in pericarditis (inflammation of pericardium).

What are the layers of the heart cavity?

The different layers of the heart protect your heart, and restrict the expansion of the heart when your blood volume increases.

Three layers of tissue that are present in your heart are:

Epicardium is the outermost thin layer that is composed of mesothelial cells, fat and elastic connective tissue. The outer layer of the pericardium surrounds the roots of your heart’s main blood vessels and is connected by ligaments to the spinal cord, diaphragm, and other parts of the body.

Myocardium is the middle layer heart muscle tissue, it also commonly known as cardiac muscle. This tissue of your heart wall actually contracts. It consists of cardiac muscles in a spiral arrangement of myocardium that squeeze blood through the heart in the proper directions inside the blood vessels.

It is the thickest layer of all the three layers and contains large number of mitochondria to provide energy to the heart muscles.

Endocardium is the deepest and innermost layer that borders the inside of the heart. It is a thin and smooth tissue that provides protection to the chambers and valves of your heart.

The inner layer of the heart walls acts as a barrier between the heart muscles and the blood circulation and contains the necessary blood vessels. It also has a cardiac conduction system, which regulates the activity of the heart muscle.

Chambers of the heart

What are the chambers of my heart?

There are four chambers in your heart: Two atria (left and right) responsible for collecting blood and Two ventricles (left and right) responsible for pumping blood. The differences in the thickness of the cardiac chamber walls are due to the difference in the amount of myocardium, which reflects the amount of force that each chamber must generate



The two upper chambers in the heart are called the atria. They are thin-walled chambers that receive blood from the veins of your body. The atrium which is on the right side of your heart is called the right atrium, it receives deoxygenated blood from the lower and upper body parts of your body; whereas the atrium which is in the left side of your heart is called left atrium, it receives oxygen-rich blood through the pulmonary veins coming from the lungs.

The right upper chamber of the heart is called the right atrium. During a normal cardiac cycle, the right atrium receives deoxygenated blood from the body (blood from the head and upper body comes through the superior vena cava, while blood from the legs and lower body comes through the inferior vena cava). When both atria are full, they contract and deoxygenated blood from the right atrium flows through the open triangular valve into the right ventricle.

The left upper chamber of the heart is called left atrium. During a normal cardiac cycle, the left atrium receives oxygenated blood from the lungs via the pulmonary veins. When both atria are full, they contract and oxygenated blood from the left atrium flows through the open mitral valve into the left ventricle


 The two lower chambers in the heart are called the ventricles. The two ventricles are thick-walled chambers that forcefully pump blood out of the heart to the lungs and your body parts.

Lower right chamber of the heart is called right ventricle. During a normal cardiac cycle, when the right atrium contracts the deoxygenated blood passes to the right ventricle of your heart. During this process, the valve in the right atrium closes, filling the right ventricle. When both ventricles are full, they contract again. The blood from the right ventricle goes to the lungs.

 When the right ventricle contracts, the triangular valve closes and the pulmonary valve opens. Closing the tricuspid valve prevents blood from returning to the right atrium and opening the pulmonary valve allows blood to flow into the pulmonary artery towards the lungs to oxygenate the blood. Right and left ventricles contract simultaneously; However, because the right ventricle is thinner than the left, it creates less pressure when it contracts than the left. This lower pressure is sufficient to pump deoxygenated blood a short distance into the lungs.

Lower left chamber of your heart is called the left ventricle. During a normal cardiac cycle, when the left ventricle contracts, it receives oxygenated blood from the left atrium through the mitral valve. At the same time, the aortic valve closes, filling the chamber with blood. When both ventricles are full, they contract. When the left ventricle contracts, the mitral valve closes and the aortic valve opens. Closing the mitral valve prevents blood from returning to the left atrium, and opening the aortic valve allows blood to flow into the aorta and from there throughout the body. The left and right ventricles contract simultaneously; however, because the left ventricle is thicker than the right, it creates more pressure when it contracts than the right. This higher pressure is necessary to pump oxygen-rich blood throughout the body.

Heart septum


What is a heart septum?

The septum is a tissue that is present in between the heart chambers, it divides the left and right sides of your heart. The main function of septum is to prevent the mixing of oxygenated and deoxygenated blood.

  • Interatrial septum – The left atria is separated from the right atria through an interatrial septum,
  • Interventricular septum – There is an interatrial septum between the left and the right ventricles.

The septum is an important tissue, which forms a barrier the four chambers of the heart. It prevents mixing of oxygenated and deoxygenated blood. In the absence of septum, the process of double circulation in your heart will not occur properly.

While the right side of the heart receives low-oxygen blood directly from the largest vein or the vena cava and sends it to the lungs via the pulmonary veins, the left side of the heart receives oxygen-rich blood from the pulmonary veins (the only veins that carry oxygenated blood from the lungs to the heart) and pumps it into the aorta (the largest artery).

Heart valves

The heart valves function as gates at the chamber entrances, opening and closing to let blood pass through. Their primary duty is to make sure that blood only flows through the heart in one direction. The valves are well adapted to withstand any physical trauma like high pressure or high velocity in blood vessels.  

The valves in your heart:
Atrio-ventricular valve

Your hearts upper and lower chambers are connected by the atrioventricular (AV) valves. It ensures that the blood flows in single direction from atrium to ventricles

The tricuspid valve opens to allow blood to move more easily from the right atrium to the right ventricles.

Blood can go from the left atrium to the left ventricle by opening the mitral valve. The mitral valve lets oxygen-rich blood from your lungs pass from the left atrium into the left ventricle.

Semilunar valve

Between the ventricles and the arteries that leave the heart are semilunar (SL) valves.

The semilunar valves are of two types: –

The aortic valve controls how much blood travels from the left ventricle to the aorta.

Right ventricle to pulmonary artery blood flow is made possible by the opening of the pulmonary valve.

Heart sound

What is the heart sound?

The valves of your heart open and close simultaneously to pass the blood, the closing of valves is a sudden process that causes surrounding fluid to vibrate and produces sound.


Two types of heart sound
  • Lub – Closure of Atrio-ventricular valve causes the first heart sound called lub. The duration of this sound is 0.1 to 0.17 second. The first heart sound is longer than the second heart sound.
  • Dub – Closure of Semilunar valves causes the second heart sound called dub. The duration of this sound is 0.1-0.14 sec. It is for shorter time than the first sound.
What is the importance of heart sound?

Your doctor listens to your heart sounds with a stethoscope to do physical examination and it is a valuable first-line tool in patient assessment.  The doctor assess the heart’s rhythm, rate, and sound of valve closure by listening carefully the sounds of heart.

Function and working of your heart

The main responsibility of your heart is to maintain a steady flow of blood throughout the body. As a result, the cells and tissues receive fresh oxygen and nutrients.

The following are the heart primary functions:

  • To circulate blood throughout the body.
  • It controls the rhythm and speed of your heart rate.
  • Blood carries nutrients including glucose, hormones, and oxygen to many bodily organs, including the human heart.
  • The heart also makes sure that your blood pressure is maintained at a healthy level.
  • Within the body, there are two different forms of circulation: pulmonary circulation and systemic circulation.
  • Your heart regulates your heart rate and other bodily processes in conjunction with other systems in the body.

Every time your heart beats, it pumps oxygen- and nutrient-rich blood around your body.  When blood returns to your heart, it flows to your lungs for oxygen. Your heart then pumps blood to the rest of your body and the process begins again.

  • Blood enters the right atrium from the superior and inferior vena cava.
  • Blood from the right atrium flows through the right AV valve (tricuspid) into the right ventricle.
  • Contraction of the right ventricle forces the pulmonary semilunar valve to open.
  • Blood flows through the pulmonary valve into the pulmonary body.
  • Blood is distributed through the right and left pulmonary arteries to the lungs, where CO2 leaves and loads oxygen.
  • Blood returns from the lungs to the left atrium via the pulmonary veins.
  • Blood from the left atrium flows through the left AV (mitral) valve into the left ventricle.
  • Contraction of the left ventricle (simultaneous with step 3) forces the aortic semilunar valve to open.
  • Blood flows through the aortic valve into the ascending aorta.
  • Blood from the aorta is distributed to every organ of the body, where it expels O and charges CO2.
  • Blood returns to the heart from the vena cava.

The main systems that regulate functions of heart are:

  • Your nervous system aids in the regulation of your heart rate. When you are at rest or under stress, it transmits signals to your heart to beat faster.
  • Your endocrine system produces and releases hormones. Your blood vessels are instructed to constrict or relax by these hormones, which has an impact on your blood pressure.
  • The hormones of thyroid gland can also command your heart to beat slow or fast.

A problem with the electrical system or the nervous or endocrine system that controls your heart rate and blood pressure can also make it harder for your heart to pump blood.

Blood is drawn from the veins and pumped to the ventricles via the atria, which have thin walls. The

heart& ventricles, which have thick walls, are responsible for pumping blood from the organ. The

valves in the the atria and ventricles together make sure that blood only flows in one direction inside the heart.

Pacemaker tissue of the heart

The pacemaker tissue in the heart is concerned with initiation (generation of impulse) and conduction of the heartbeat.

The three basic parts of the pacemaker tissue are: –

  1. Sino Atrial Node (SAN)
  2. Atrio – Ventricular node (AVN)
  3. Atrio – Ventricular Bundle/ Bundle of His
  4. Purkinje fibers
Sino Atrial Node (SAN)

Sino-Atrial node is the natural pacemaker of your heart, it is a small mass of specialized fibrous tissue that can generate and discharge impulses more rapidly than any other pacemaker tissue and their rate of discharge of impulse in heart muscles determines the rate at which the heart beats.

SA node is a thin elongated muscle fibre, which is rich in glycogen and mitochondria. It is highly vascular and also called pacemaker cells. It is located at the junction of the superior vena cava with right atrium. Pathways. They conduct impulses from ‘SA node’ to the ‘AV node’ by arranging themselves in 3 bundles.

The modified atrial muscle fibres from the region of coronary sinus collect fanwise and unite with the ‘AVN’ called internodal atrial pathways. They conduct impulses from ‘SA node’ to the ‘AV node’ by arranging themselves in 3 bundles.

  • Anterior internodal tract of Bachmann (It can also conduct impulses from ‘SA node’ to ‘Left atrium’)
  • Middle internodal tract of Wenckebach
  • Posterior internodal tract of Thorel

The slow conduction in SA node and AV node is caused by decreased numbers of gap junctions between the successive cells in the conducting pathways.

Atrio-Ventricular node (AV Node)

Atrio-Ventricular node is commonly known as AV node. It is considered as the secondary pacemaker of your heart.

AV node is a specialised mass of cells which has the ability of self-excitation. It has the primary function transmitting impulse to the ventricles. It can produce electrical impulse and conducts it from atria to ventricles of your heart.

AV node is located on the right side of the interatrial node near the opening of coronary sinus of your heart.  The structure of AV node is quite similar to the structure of SA node.

Atrio – Ventricular Bundle/ Bundle of His

The bundle of his originates from the AV node, it is a group of fibers that carry electrical impulses through the center of the heart.

The bundle of His is an elongated segment that connects the AV node and the left and right bundle branches of the septal crest. In an adult heart, it is approximately 1.8 cm long and is mainly located deep in the dense connective tissue. The bundle of His lies adjacent to the annulus of the tricuspid valve, distal to the atrioventricular loop and slightly close to the right bundle branch and the left bundle branch.

The bundle of his is divided into a right and left branch.  The left branch pierces the membrane and then lies on the upper border of the muscular septum to divide into an anterior fascicle and a posterior fascicle. The right branch passes down the right side of the septum.

Both the branches divide repeatedly to form a network of fibres lying in the ventricles.

Purkinje fibers

Purkinje fibers originate from terminal divisions of right and left branch of the Bundle of His to penetrate the ventricular wall.

They are larger and thicker than the SA node, the length is 10-46 micrometer and 70-80 micrometer.

Purkinje fibers have large diameter, it transmits the impulse at a fast velocity of 4mts per second. This allows almost immediate transmission of the impulse throughout the entire ventricular system.

Heart Rate

Heart rate is how many times your heart beats per minute. Your body automatically controls your heart rate based on what you are doing or what is happening around you. Therefore, your heart rate increases when you are active, excited, or fearful, and decreases when you are resting, calm, or comfortable.

Heart rate is regulated by two branches of the autonomic nervous system (involuntary). Sympathetic nervous system and the parasympathetic nervous system are two types of autonomic nervous system. Hormones (catecholamines – epinephrine and norepinephrine) are released by the Sympathetic nervous system to increase heart rate.

Heart rate is also an important indicator of your overall health. If your heart rate is too fast or too slow, it could be a sign of heart or other health problems. Sensing heart rate throughout the body is also a possible way for doctors to diagnose disease.

The doctors use stethoscope to know about your heart rate, heart sounds and on basis of that take diagnose further.

A normal heart rate ranges from 60 to 100 beats per minute. This is known as resting heart rate.

The heart rate can change as per your activities, if you do more of physical activity your heart rate increases to supply your muscles with more oxygen.

For instance, your heart rate will be substantially higher while you are running or exercising than when you are sitting calmly at one place. At this time, the heart rate is in between 120- 160 beats per minute or more.

Few basic factors that influence heart rate: –

  • Age
  • Exercise
  • Emotions
  • Stress
  • Medication (if any)

Your pulse is the rhythmic expansion and contraction of an artery caused by the impact of blood pumped by the heart. Your heart pumps blood throughout your body each time it beats. This heartbeat that can be felt on your neck or wrist is known as pulse.

The number of times your heart beats in a minute is used to calculate your pulse. Your pulse would be 72 beats per minute, for instance, if your heart beats 72 times in a minute (BPM). The heart rate can be another name for this.

To check the pulse at the wrist, place two fingers between the bone and tendon above the radial artery (located on the thumb side of the wrist).

 When measuring the pulse:
  • Press the first and second fingertip firmly but gently on the arteries until you feel the pulse.
  • If you feel a pulse, count the number of beats in 15 seconds.
  • Calculate the beats per minute by multiplying this number by four.
  • When counting, do not constantly look at the clock, but focus on the pulse beats.
  • If you are unsure of your results, ask someone else to do the count for you.

There is a relationship between your heart rate and your heart rate, but they are not the same. Your heart rate shows how fast your heart is beating at any given moment. Pulse is the way you feel how fast your heart is beating.

Heart pressure

Your blood pressure is the force exerted by the blood on the walls of your blood vessel as the heart pumps (contracts) and relaxes. If the pressure is too high, you can have serious health complications.

Your blood pressure reading has two measurements:
  • Systolic blood pressure (top/first number): This is the pressure in your arteries when your heart beats and sends blood into your arteries.
  • Diastolic blood pressure (bottom/second number): This is the pressure in your arteries when your heart is resting between heartbeats.

The normal blood pressure range is 120/80 mm hg.

If your blood pressure increases or decreases below this level, you must consult your doctor immediately.

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