Heart and its working

In an adult, the pacemaker makes almost 72 impulses in a minute in the rest condition; it means that in one minute the heart goes through a full cardiac cycle around 72 times. Normally, as good the physical fitness of an individual is, as slower the heart rate at rest will be. Some of the very good athletes are known to have a pulse rate of 35 beats per minute which is half the average figure for the general population. For them, the slow heart rate is enough and does not make any danger.
As the lungs are very close to the heart and the walls of the pulmonary vessels, which are thinner so offer less resistance, the right ventricle does not have to exert nearly as much energy to do its job of supplying blood to the lungs as the left ventricle does in supplying to the rest of the body, is known as the cardiac output. When there is a requirement for an increased blood supply, as during physical stress, the heart most increases its output by beating faster. This mechanism has its limits: Above a certain rate, the heart chambers do not have time to fill properly and fail to pump efficiently.

The cardiac output is examined by the heart rate as well as by the amount of blood that ventricles eject or pump out in each contraction. This amount is known as the stroke volume. Usually the ventricles force about half the blood they contain, which corresponds to about 3 ounces in an average person at his rest position. A decrement in the stroke volume is one of the first signs of a heart failing. When both ventricles pump out, the same amount of blood in each stroke, cardiologists usually measure only the stroke volume of the left ventricle.