The combination of captopril and nitroglycerin early after acute myocardial infarction (AMI) could lead to a dangerous decrease in blood pressure coronary perfusion. To evaluate the safety aspects and haemodynamic effects of this combination, we studied 36 first 'Q wave' thrombolysed anterior wall AMI patients during the 24 h following the onset of symptoms. Afterwards, thrombolysis patients received a continuous infusion of nitroglycerin and were submitted to pulmonary artery catheterization. Those patients with mean arterial pressure (MAP) > or = 70 mmHg, cardiac index > or = 2.2 l.min-1.m-2, and wedge pressure > or = 10 mmHg were included and randomized to receive 6.25 mg of captopril every 6 h on the first day and 12.5 mg qid on the second if MAP > or = 70 mmHg (group 1). A second group (group 2) received a placebo. Haemodynamic parameters were determined after 1, 6 and then every 6 h up to 48 h after basal measurements. Significant differences were observed only for the MAP and the rate-pressure product (reduction in group 1 values, P < 0.05). However, MAP was maintained within acceptable limits. Our data support the fact that the combination of captopril and nitroglycerin in the early hours of a non-complicated anterior wall AMI is safe, and could guarantee its use in large clinical trials to determine the effects on left ventricle remodelling and survival after AMI.