Stethoscope. A stethoscope on a white lab coat. A stethoscope is used to listen to sounds within the human chest. It consists of two earpieces, tubing, and a round sound-detecting device with diaphragm (bottom). By pressing the diaphragm against a patient's chest, sounds made by the heart and lungs can be detected. A stethoscope is useful in diagnosing respiratory ailments of the lungs, and abnormalities of the heart.