Echocardiography has proved useful for cardiac diagnosis during the past several years; however, the conventional one-dimensional ultrasound pulse echo method cannot easily visualize the anatomical relationships of the various cardiac structures. To overcome the limitation, the authors attempted a real-time observation of cardiac structures and introduced high-speed ultrasonocardiotomography with a Sonolayergraph Model SSL-51H (Toshiba) having a logarithmic amplifier. Thirty sector images are produced per second by a mechanically operated, single flat or 75 mm. focus transducer measuring 10 mm. in diameter. The angle of a sector image composed of about 120 scanning lines is arbitrarily changeable from null to 65 degrees. The fast succession of images produced enables clear observation of the movement of cardiac structures in real time. Study of 230 patients by means of the proposed system suggests that it is advantageous as a quick method to provide two-dimensional echocardiograms for cardiac diagnosis and assessment, especially in noninvasive diagnosis.