Arrhythmias are frequent complication in patients with acute myocardial infarction (MI). The importance of accelerated idioventricular rhythm (AIVR), ventricular fibrillation or tachycardia (VF, VT), atrial fibrillation or flutter (AF) and bradycardias is considered and discussed in this review article. The value of the presence of AIVR as a marker of reperfusion is small, but in combination with other non-invasive markers (ST-segment resolution), its presence is connected with a high probability of successful reperfusion. Early ventricular arrhythmias are a serious complication of MI. However, if they are revealed and treated in time, they apparently do not represent a negative prognostic factor. Later occurred VF or VT are more a symptom of larger MI. AF, which is not directly life-threatening for the patients, frequently occurs in patients with larger MI and it is an independent predictor of a poor long-term prognosis of these patients. The early and successful reperfusion therapy is the best anti-arrhythmic therapeutic method in patients with MI.