Twenty patients (age 45 to 78 years) were studied with ethical committee approval and informed patient consent during coronary artery bypass grafting. Transesophageal echocardiography (TEE) was used to validate a clinical measure of preload: inspection of the line of contact between the heart (acute margin) and the diaphragm. Immediately before going on cardiopulmonary bypass (CPB), with the cannulas and stay sutures in place, a small mark was made with the cautery on the diaphragm at the line of contact. After CPB the patients were transfused from the extracorporeal circuit to exactly the same level. At these two times, TEE recordings of the short axis of the left ventricle were performed and stored on videotape for later blinded evaluation off-line. The left ventricle short-axis area in end-diastole measured after CPB showed a close correlation to that measured before CPB, r = 0.88, P < 0.001. The regression line was close to the line of identity. The conclusion was that inspection of the line of contact between the heart and the diaphragm can be used clinically during weaning from bypass to obtain the same left ventricular end-diastolic volume as before CPB.