Stethoscope. View of a stethoscope and an electrocardiogram trace (ECG). A stethoscope is a medical instrument used for listening to sounds within the human chest. It consists of two earpieces (not seen here), tubing (top right corner), and a round sound-detecting device with diaphragm (upper centre). By pressing the diaphragm against a patient's chest, sounds made by the heart and lungs can be detected. It is useful in diagnosing ailments of the lungs and heart. An ECG is a record of the electrical impulses of the beating and relaxed heart muscle. It is used to diagnose irregularities and disorders of the heart.