What is Heart| Internal Structure|



Do you wonder how the human heart works?…

Don’t worry in this blog, I will be talking about the Heart, its structure, it’s working, and the conduction of impulses.

I am here talking about an actual heart structure, not the one which every other lover is imagining off… or every

other Bollywood movie describes the heart like “ Dil Hai Ki Manta Nahi“…

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I am talking about the above heart, not the below one


Just kidding..!!!

Let’s get started


the internal heart


What is Heart?…


human heart location

The Heart is a pumping organ.

The heart has a very complex structure after the human brain

The average weight of the heart in adult men ranges from 280 to 320g differ with length and height.

It is a middle layered muscle (Myocardium) that is situated slightly towards the left of the chest while the Epicardium and Pericardium protect it (Heart) from injuries.


Internal structure of the human heart:


human heart anatomy


The human heart is a 4-chambered organ, namely the right atrium, right ventricle, left atrium, and the left ventricle

Interesting Trivia: Giant Pacific Octopus has 3 hearts, 9 brains and blood is blue in color

Respective atriums are situated upperside whereas the respective ventricles are situated in the lower part of the heart

The right part of the heart is differentiated from the left part with the help of the Diaphragm also called Septum as can be seen in the diagram below.


human heart


The Atrium is separated by the ventricle with the help of valves.

Valves basically prevent the backflow of blood.

The Right atrium is separated from the right ventricle by Tricuspid Valve whereas,

the left atrium is separated with the help of the Bicuspid Valve.

The Atriums are smaller in size while the ventricles are thicker and

broader in size as they pump the blood against gravity.

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Physiology of Heart:




human heart diagram


Human Heart (1)


Referring to the above image, the blue part represents the flow of deoxygenated or impure blood, and the red part represents the oxygenated or pure blood.

In simple terms, deoxygenated means less or zero amount of oxygen, and oxygenated means a high amount of oxygen.


human heart rate


1) What is Pulmonary Circulation?

As we can see, the Superior vena cava and inferior vena cava bring back the

deoxygenated blood from the upper part and

the lower part of the body respectively into the right atrium.

Here, vena cava is a large pipe-like organ or in simpler terms larger form of veins.

Generally, Arteries carry oxygenated or pure blood and Veins carry impure blood

but in the case of the heart, the pulmonary artery carries impure blood and

pulmonary veins carry pure blood.

As soon as the impure blood comes into the right atrium,

the right atrium contracts and the blood goes to the right ventricle through Tricuspid Valve.

Tricuspid means having three cusps or leaflets.

The impure blood from the right ventricle goes to the lungs through the pulmonary valve via the pulmonary artery.

Pulmonary means related to the lungs.

So till here, this is also called Pulmonary Circulation.


1) What is Systemic Circulation?

The purification process completes in the alveoli sacs of the lungs. (Will see the process in the lungs blog)

The pureblood enters the left atrium through pulmonary veins from the lungs.

Then left atrium contracts, the mitral valve or bicuspid valve will open and the blood will enter the left ventricle.

The left ventricle contracts and the aortic valve opens and through the systemic aorta, the pureblood is supplied to different parts of the body.

And this completes the Systemic Circulation

So, the process of supply of the blood from the body to the heart and again back from the heart to the various parts of the body is called Double Circulation

Every above-mentioned process takes just 0.8 seconds to complete and this process continues from the time you born and lasts till your last breath

human heart images


Electrical conduction system of the heart:



Conducting system of heart
Conduction system of Heart(1)


Conducting System of Heart(2)


Conducting system of Heart consists of 4 main parts, It includes


1)SA node i.e., Sino-Atrial Node which is known as a natural pacemaker of the Heart

2) AV Node i.e., Atrio-ventricular Node.

3)Bundle of His.

4)Purkinje Fibres.


  • SA node: Located in the top-most of Right Atrium as shown in the figure, initiates the impulses for the contraction of atria/auricles.


  • AV node:  As named located in the middle diaphragm of the heart controls heart rate and conducts impulses.


  • Bundle of His:  Named after the Scientist His who was responsible for the discovery of the thread-like structure transmit impulses from AV node to ventricles,    is located just below the AV node and is spread over the edges of the ventricles


  • Purkinje fibers:  are the end terminal network that receives impulses from the AV node to ventricles.

The impulses are generated in the Natural Pacemaker i.e, Sino-Atrial Node due to the phenomenon known as Action Potentials. It is a phenomenon that is generated due to the exchanging of chemical ions namely Potassium (K+)and sodium(Na+) and Chlorine(Cl-)

ecg test

ecg meaning

Electrocardiograph (ECG)

It is an instrument to measure the electrical activity of the heart for various Heart-related Diseases.

When somebody is suffering from any heart-related disease.

The doctor says,” Go and take an ECG test”.

After seeing the ECG report, The doctor concludes that the patient is suffering from ABC disease.

So It is a diagnostic technique and not a therapeutic technique.

In some places, it is denoted as EKG but the technique is the same

The alternative to ECG is TMT i.e, (TreadMill Test)

But It is slight discomfort for the patient to run on a treadmill

And also there are Motion Artifacts i.e, Noise in the signal due to continuous motion.






  • The p wave represents the Contraction of Auricles/Atria


  • The QRS complex represents two major events i.e., relaxation of the atria and contraction of Ventricles simultaneously.


  • T wave represents the relaxation of the ventricles


  • Any defect in the standard wave diagnoses that the subject (patient) is suffering from the Heart problem

ecg lead placement



NOTE: To explain to you in simple terms and to avoid any confusion I have explained every chamber process separately but the contraction and relaxation of both auricles and both ventricles are done simultaneously. When both auricles contract, both ventricles are at rest, and vice versa.

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