If short pulses of high frequency sound are transmitted through the heart, discontinuities in the tissues will produce reflected sound waves or "echoes". There wil! be a delay between a pulse transmission and the arrival of a correspond·mg echo. Together with knowledge of sound velocity this wi!l enable determination of the distance between the transmitterfreceiver and the reflecting interface, thus providing information about cardiac dimensions. Similarly the Doppler effect can be used to provide further diagnostic information. These applications of ultrasound (echocardiography) for the detection of cardiac (mal)function have recently gained acceptance even though interpretation of the information obtained can be difficult. Major reasons for this acceptance are probably that, while the techniques provide information that otherwise is not available, most of the applications involve .non-invasive methods and are well tolerated by the patient. In addition reports in the literature indicate that, at diagnostic intensity levels, the technique seems to be free from hazard.