We evaluated the presence of thromboxane B2, the stable metabolite of thromboxane A2, early in the course of acute myocardial infarction (AMI) in both animal and patient studies. In an open-chest model, the left anterior descending artery (LAD) was isolated and the great cardiac vein was cannulated in nine dogs. Following occlusion of the LAD, there was an increase in thromboxane B2 concentration from 0.77 +/- 0.0093 to 1.79 +/- 0.46 pmol/ml (p less than 0.05) and 1.96 +/- 0.48 pmol/ml (p less than 0.05) at 1 and 5 minutes, respectively, following coronary occlusion. At 30 and 60 minutes after occlusion there was no significant increase compared to the baseline. In 17 patients with AMI the mean thromboxane B2 concentration was 0.96 +/- 0.13 pmol/ml at 4.88 +/- 0.40 hours after the onset of chest pain. In 12 patients with sequential samples before and after restoration of patency of the occluded vessel, the initial concentration was 0.71 +/- 0.058 pmol/ml. At 5 minutes after restoration of patency thromboxane B2 concentration was 1.1 +/- 0.17 pmol/ml (p = 0.05). One hour later a return to baseline was noted (0.82 +/- 0.75 pmol/ml). Two patients with the highest thromboxane B2 concentrations (2.0 and 2.6 pmol/ml) were unable to have successful recanalization. We conclude that generation of thromboxane A2 occurs during the early stages of AMI and may be an important pathophysiologic phenomenon in AMI.