Reperfusion therapy has lowered mortality in patients suffering from acute myocardial infarction. Failure to reperfuse is associated with an increased short- and long-term mortality. In a prospective study we used dynamic vectorcardiography to monitor 96 patients with acute myocardial infarction treated with reperfusion therapy to non-invasively assess coronary patency. The results from continuous monitoring were compared to those obtained from angiography. By using trend-analysis of QRS vector difference and ST vector magnitude, we were able to correctly identify 58 of the 70 patients (83%) with a reperfused infarct-related artery, and 19 of the 26 patients (73%) with a persistently occluded artery demonstrated at an early angiogram (diagnostic accuracy 80%). In patients with high-grade collateral flow to the infarct-related area, the results of the vector cardiographic monitoring and of angiography showed the largest disagreement, whereas the accuracy of vector cardiographic monitoring was high: 88%) among patients without collaterals. The present results suggest that QRS complex and ST segment vector cardiographie monitoring is a useful tool for assessing early coronary artery patency, and that dynamic vectorcardiography may help in identifying candidates for emergency coronary angiography.