Heart Sound:
The sounds heard over the cardiac region produced by the functioning of the heart. There are four distinct sounds: the first occurs at the beginning of systole and is heard as a “lubb” sound; the second is produced by the closing of the aortic and pulmonary valves and is heard as a “dupp” sound; the third is produced by vibrations of the ventricular walls when suddenly distended by the rush of blood from the atria; and the fourth is produced by atrial contraction and ventricular filling but is rarely audible in the normal heart. The physiological concept of HEART SOUNDS is differentiated from the pathological HEART MURMURS.
