diagnostic technique that uses ultrasound (high-frequency sound waves) to produce an image of the internal structures of the heart. A piezoelectric transducer placed on the surface of the chest converts electrical impulses into a narrow ultrasonic beam that penetrates body tissues but is reflected off surfaces where a change in tissue density occurs. The reflected sound waves are detected by a receiver also placed on the chest, transformed back into electrical impulses, and projected on the screen of a cathode-ray oscilloscope. Echoes from varied depths produce an image of the walls and valves of the heart and of their motions. Such information can aid in diagnosing valve disease, congenital heart defects, and other cardiac abnormalities.