Heart is a muscular organ that pumps blood to all the parts of the body. Heart pumps blood which is rich in oxygen and nutrients into the circulatory system. This system consists of blood vessels, such as arteries, veins, and capillaries which take blood that is pumped from heart into organs and receive blood from organs to heart. Heart consists of an electrical system which uses electrical signals to contract the heart’s walls. When the walls contract, blood is pumped into the blood vessels. Heart is located under the rib cage in the centre of the chest between the right and left lungs. The size of the heart can vary depending on the age and size. A normal, healthy, adult heart usually is the size of an average clenched adult fist. It may enlarge in diseased conditions of the heart.

How the heart works

After the body’s organs and tissues have used the oxygen in the blood, the large veins called venae cavae carry the oxygen-poor blood back to the right side of the heart. The upper vein (superior vena cava) carries oxygen-poor blood from the upper parts of the body and the lower vein (inferior venae cava) carries from the lower part. Oxygen-poor blood from the vena cavae flows into the heart’s right side and then pumped to lungs via a blood vessel called pulmonary artery.

Once in the lungs, the blood travels through many small, thin blood vessels called capillaries. There, the blood picks up more oxygen and transfers carbon dioxide to the lungs—a process called gas exchange. The oxygen-rich blood passes from the lungs back to your heart’s left side and from there pumped all over the body.

How the heart works

Heartbeat

All of us might have heard or known that when heart beats, it makes a “LUB-DUB” sound. Between the time we hear “LUB” and “DUB,” blood is pumped through the heart and circulatory system. A heartbeat consists of a complex series of very precise and coordinated events. Each heartbeat reflects two important components of heart’basic functions; they are systole or the phase of heart’s contraction, when blood flows from the heart to all the parts of the body and diastole or relaxing phase when heart gets filled up from the blood from all the parts of body.

Contraction phase

As the ventricles get filled up from the oxygen poor blood from the organs and tissues in case of right ventricle and oxygen rich blood from lungs in case of left ventricle, both these ventricles contract or squeeze and push blood into the lungs in case of right ventricle and all over the body in case of left ventricle.

Relaxation phase

After the contraction or squeezing of the blood, both ventricles relax and allow the blood to fill, both the ventricles.

Pulse

When the heart pumps blood through the blood vessels, it causes a wave front that can be felt on the blood vessels in the different parts of the body. But usually we feel the pulse on the wrist, because of ease of identification and the superficial position of this blood vessel (radial artery) .At this place we can count the pulse, and identify how many times it is felt in a minute. The usual resting pulse for an adult is 60 to 100 beats per minute. Any pulse rate less than 60 per minute or more than 100 per minute can be abnormal, and this is called bradycardia and tachycardia respectively.

Heart’s Electrical System

Electrical system of the heart, which is also called cardiac conduction system, is behind the contraction and relaxation by which heart pumps blood to all over the body. Electrocardiogram also known as ECG records this electrical events from the surface of the body. Heart’s electrical system consists of mainly- 1. Sinoatrial node or SA node, which is called pacemaker of the heart, the heart beat originates and spreads all over the heart. 2. This goes to another structure called Atrioventricular node or AV node, which transmits the heartbeat from the upper chamber (atrium) to the lower chamber (ventricle). 3. From the AV node the heart beat gets conducted to two wires called bundle branches and through this structures both the ventricles receive the heart beat and both the ventricles contract and pump the blood.

The S-A node normally produces 60-100 electrical signals per minute — this is the heart rate, or pulse. With each pulse, signals from the S-A node follow a natural electrical pathway through the heart walls. The movement of the electrical signals causes the heart’s chambers to contract and relax. In a healthy heart, the chambers contract and relax in a coordinated way, or in rhythm. When the heart beats in rhythm at a normal rate, it is called sinus rhythm. The left ventricle contracts an instant before the right ventricle. This pushes blood through the pulmonary valve (for the right ventricle) to your lungs and through the aortic valve (for the left ventricle) to the rest of your body. As the signal passes, the walls of the ventricles relax and await the next signal. This process continues over and over as the atria refill with blood and more electrical signals come from the SA node.

When working well, the conduction system automatically responds to the body’s changing need for oxygen: When we climb stairs, carry heavy objects, or take a walk, we need more oxygen; therefore, the heart beats at a faster heart rate. When we are sitting or sleeping, we need less oxygen; therefore, the heart beats at a slower rate. The conduction system senses the need for oxygen and responds with the proper heart.