Human heart consists of 4 chambers, 2 atria and 2 ventricles. In human cardiovascular system is closed, with oxygenated blood in arteries and deoxygenated blood in veins, reverse is seen in pulmonary circulation. The oxygenated blood pumped from ventricles travel via big aorta to small arteries by pumping mechanism of heart and in tissues exchange occurs at capillaries level, and then deoxygenated blood carried back via veins, superior and inferior vena cava to right atria. The deoxygenated blood from tissues gets oxygenated in pulmonary circulation. The pumping action of heart is maintained via its contractibility of muscle fibers, triggered by the rhythms from SA node.

The impulse so generated travelled via conducting fibers of atria, AV node, bundle of hiss and purkinje system to ventricles. Thus the contraction maintained by the contractile system of heart makes the blood flow in vessels through aorta to whole of the body. The pressure thus generated in vessels is recorded as blood pressure with systole and diastole, as during contraction and relaxation phase. The electrical rhythm generated from SA node to ventricles is recorded as ECG. Problem in rhythm of heart may lead to arrhythmias.  The heart itself derives its oxygen and nutrient primary from coronary vessels derived from aorta.

The narrowing of vessels by atherosclerosis (deposition of fat) or spasm of vessels decreases the blood flow to tissues and may causes angina pectoris, stroke or other ischemic diseases. The blood in vessels usually flows in laminar pattern, and increase in viscosity of blood might decrease its flow rate. Increase in intravascular coagulation may also hamper the blood flow.