The heart is divided into right and left sides. Each side has a chamber that receives blood that is returning to the heart (called atria) and a muscular chamber that is responsible for pumping blood out of the heart (called ventricles).
Blood that has traveled to parts of the body and is now oxygen poor returns to the heart and enters the right atrium. This blood is then pumped by the contraction of the rightatrium in to the right ventricle. The right ventricle in turn contracts and pumps this blood to the lungs, where it absorbs oxygen. The oxygen’s rich blood then returns from the lungs to the heart and enters the left atrium, where it is pump into left ventricle. The left ventricle is the most muscular of the heart’s chambers and serves as the main pumping chamber of the heart. When the muscular tissue of the left ventricle contracts blood is pumped into the aorta, the main artery of the body, which supplies blood to other arteries. Oxygen’s rich blood travels through the aorta to other arteries of the body and then, in turn to the organs and tissues of the body, which require oxygen to function. Oxygen’s poor blood returns from these organs and tissues through the veins back to the right atrium of the heart, and the cycle repeats itself.
The contraction of the different chambers of the heart are normally organized in a very specific manner, a special type of electrical impulse travels through the heart and sets off contractions in the chamber as it passes through the chambers.
The hearts normal spark plug is an area of specialized tissue called the SA node which is located in the right atrium. Each time this tissue fires, an electrical impulse is generated that travels first through the right and left atria, signaling these chambers to contract and pump blood into the ventricles. The impulse then travels down into another small patch of specialized tissue called the AV node, which is located between the atria and the ventricles. The electrical impulse is conducted through the AV node and then through specialized pathway into the ventricles, where it signals the ventricles to contract and to pump blood out into the lungs and through the body, the normal sequence of electrical activation of the chamber of the heart is called sinusrhythm. This sequence occurs each time the heart beats, usually about 60-80 times per minute.