In conventional cross-sectional echocardiography, the configuration of the chest or the presence of excessive chest wall tissue or air-containing lung often limits the resolution and field of view. To increase the diagnostic capability of cross-sectional echocardiography, a transesophageal ultrasonic high speed rotating scanner that can obtain cardiac images without hindrance from ribs, sternum and lung was developed. The scanner uses a single small transducer with a flexible shaft to permit easy swallowing by adults and mechanically scans ultrasonic beams within the esophagus. The small transducer in the esophagus is rotated through a full 360 degrees at a rate of 15 to 50 cycles/s, and cardiac images obtained through the esophageal wall are displayed on a cathode ray tube in real time. The transesophageal scanning technique was evaluated in more than 50 adult patients. Aside from some slight gagging, no serious complications were encountered. In all patients, high quality images of most portions of the heart were obtained. There was little difference in the image quality among various patients.