Reperfusion therapy has lowered the mortality in patients suffering acute myocardial infarction. Failure to reperfuse is associated with significantly higher risk of short- and long-term mortality. Detection of reperfusion is thus important. In a prospective pilot study, we used continuous on-line computerized vectorcardiography to monitor 21 patients with acute myocardial infarction treated with reperfusion therapy to noninvasively detect coronary patency. By using trend analysis of QRS vector difference, we were able to correctly blindly identify 15 of 16 patients with a perfused infarct-related artery and four of six patients with a persistently occluded artery at an early angiogram. The present results are based on a limited number of patients, but suggest that QRS complex and ST segment monitoring with continuous on-line vectorcardiography has substantial potential for monitoring patients with acute myocardial infarction treated with reperfusion therapy.