Patients with a patent coronary artery after reperfusion therapy show an increased rate of evolution of QRS changes and of resolution of S-T changes as compared to patients with a persistent occlusion. Dynamic vectorcardiography permits multi-lead monitoring of changes in QRS complex and S-T segment over time. We monitored 150 patients randomized to alteplase or streptokinase for 24 h after admission. Alteplase was associated with significantly more rapid evolution of electrocardiographic changes but also with an increased occurrence of recurrent S-T changes. This may indicate a higher rate of early reperfusion with alteplase but due to recurrent ischemia, an electrocardiographic catch-up is seen with similar extent of myocardial damage observed after 24 h of monitoring.