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CARDIAC SOUND
The sounds heard over the cardiacregion 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 atrialcontraction and ventricularfillingbut is rarely audible in the usual heart. The physiologicalconcept of heart sounds is differentiated from the pathologicalheart murmurs.