The role of transoesophageal echocardiography in the diagnosis of ventricular septal defect in the acute stage of myocardial infarction, was evaluated in 15 consecutive patients (10 men and 5 women) with a mean age of 72 years in the period between June 1991 and April 1995. The patients had 11 anterior infarcts and 4 inferior infarcts with extension to the right ventricle. One patient was in Killips class I,7 patients in class II, 2 in class III and 5 in class IV. Only 8 of the 15 septal ruptures could be visualised directly by conventional transthoracic echocardiography, though all 15 were suspected from continuous Doppler and colour Doppler analysis. Transoesophageal echocardiography was successfully performed in 14 of the 15 patients with a monoplane probe in 11 cases and a multiplane probe in 3 cases. The average duration of the procedure was 12 minutes and clinical and haemodynamic tolerance was good. Ventricular septal defect was directly visualised in all cases in the short axis transgastric view and in 7 cases in transoesophageal views. Transoesophageal echocardiography was concordant with peroperative findings with regards to the site of ventricular septal defect (8 apical, 5 postero-basal and 1 median), their type (6 punched-out defects, 5 fissures, and 3 perforated aneurysms), their size (average 9.3 mm), their number with 5 multiple defects, and associated lesions (4 right ventricular extensions, 4 hemopericardiums and 1 free wall fissure). Transoesophageal echocardiography completes traditional transthoracic echocardiographic examination in the diagnosis of post-infarction ventricular septal defect. It is well tolerated and, in the authors' experience, allows limitation of invasive procedures to coronary angiography alone.