Myocardial reperfusion is associated with a number of clinical, electrocardiographic (arrhythmias, conduction defects, ST segment changes), haemodynamic and biological events. The commonest arrhythmias are ventricular extra-systoles, rapid ventricular tachycardias, and accelerated idio-ventricular rhythms. Reperfusion bradycardias are less common. When the arrhythmia is related to ischaemia it usually regresses when perfusion is restored. Reperfusion of the inferior wall of the left ventricle is often associated with sinus bradycardia and hypotension. The ST segment changes may evolve in two different ways: progressive regression or accentuation of ST elevation. When the responsible artery is recanalized, there is an immediate rise in plasma enzyme and myoglobin concentrations. The peak CPK concentration is usually observed after the 12th hours. The diagnostic value of the reperfusion syndrome lies in the interpretation of rapid ventricular tachycardias, accelerated idio-ventricular rhythms, ST segment changes and immediate rise in plasma CPK levels. The clinical risks of the reperfusion syndrome are low, practically never rhythmic and only exceptionally haemodynamic.