The mechanism of forward blood flow during closed chest cardiac massage remains controversial. Two theories have been suggested: the cardiac pump theory and the thoracic pump theory. Case report is presented to illustrate the use of transesophageal echocardiography during cardiopulmonary resuscitation. The findings included right and left ventricular compression, closure of the mitral valve during compression, opening of the mitral valve during the release phase, and atrioventricular regurgitation during compression, indicating a positive ventricular-to-atrial pressure gradient. These findings suggest that direct cardiac compression was the predominant mechanism of forward blood flow during cardiopulmonary resuscitation in this patient. Transesophageal echocardiography offers a new approach for study of the flows and cardiac morphologic features during chest compressions in humans. An understanding of the actual mechanisms involved is necessary if improved cardiopulmonary resuscitative techniques are to be rationally developed for enhancing the outcome of resuscitation.