heart sound, a noise produced within the heart during the cardiac cycle that can be heard over the precordium. It may reveal abnormalities in cardiac structure or function. Cardiac auscultation is performed systematically from the apex to the base of the heart or from base to apex, using a stethoscope to listen, initially with the diaphragm and then with the bell of the instrument. Standard heart sounds include S1, produced by the closure of the atrioventricular valves; S2, produced by the closure of the semilunar valves; S3; and S4. Additional heart sounds include clicks, gallops, murmurs, rubs, and snaps.
