Cardiovascular system starts with the heart, as heart is major organ in this system. The function of heart determines the functional status of the body. Any physical or functional abnormalities in heart leads to decrease in heart function. So, to know physiology of heart is important. It is the pumping organ which supplies oxygen and nutrients throughout the body constantly, never pausing. Powered by muscles and perfectly synchronized by electrical signals, it's one of nature's finest feats of engineering. SA node acts as natural pacemaker that regulates the heart rhythm.
The American Society for Preventive Cardiology; American Society of Nuclear Cardiology; American Heart Association; ACC; American Stroke Association; Society for Cardiovascular Angiography and Interventions.