The heart works as a pump. The deoxygenated blood from the body tissues arrives to the right atrium via the superior vena cava and the inferior vena cava. When the right atrium is filling, the tricuspid valve opens and let the blood flow into the right ventricle. After that the right atrium contracts and pushes the remaining blood into the right ventricle. Then the right ventricle contracts and pumps the blood into the pulmonary artery by opening the pulmonary valve. The pulmonary valve closes after that. Then the blood get oxygenated by the lungs and return to the heart via the pulmonary veins. Pulmonary veins carry blood to the left atrium. Then the bicuspid valve opens and let the blood flow into the left ventricle. After that the left atrium contracts and pushes the remaining blood to the left ventricle. After that the left ventricle contracts and closes the bicuspid valve and opens the aortic valve. Then the blood gets pumped into the aorta. After pumping, the aortic valve gets closed. The function of the heart is managed and operated by electrical signals. We can detect the heart’s electrical activity by an ECG.
The heart cycle
The heart cycle is the sequence of events that takes place in a complete heartbeat. In this process one complete cycle of filling and pumping blood occurs. One complete heart cycle takes 0.8 seconds to complete. The heart cycle occurs as, atrial systole, ventricular systole, and complete cardiac diastole. When at rest, a healthy heart will beat about 60-80 beats per minute. The atrial systole means contraction of atria. The atrial systole takes about 0.1 seconds. When the blood flows into the atrium, the SA node gets stimulated. As a result, the SA node triggers the contraction of the atrium myocardium, that pushes blood into the ventricles, by emptying the atria. The ventricular systole means contraction of the ventricles. This takes about 0.3 seconds. In this, a wave of contraction sweeps upwards from the apex of the heart. As a result, both ventricles get contracted. This will rise the pressure inside the ventricles. As a result, both the pulmonary valve and the aortic valve gets open and, the blood will flow into the pulmonary artery and the aorta, respectively. In the complete cardiac diastole, both the atria and the ventricles get relaxed. The complete cardiac diastoles take about 0.4 seconds. When the ventricles are relaxing, the pressure inside the ventricles will be lower than the pressure inside the pulmonary artery and the aorta. As a result, the pulmonary valve and the aortic valve closes by preventing blood being flow back to ventricles. When the atria are relaxing, the blood the superior and the inferior vena cava carries blood into the atriums. This increases the pressure inside the atriums. As a result, the tricuspid and the bicuspid valves get opens and the blood will passively flow into the ventricles.