One hundred and one consecutive post-myocardial infarction (MI) patients were investigated with 24-h long-term ECG registration (LTER), exercise test and radionuclide angiocardiography (RNA) within one month of the MI and after six and 12 months. Patients with low left ventricular ejection fraction (LVEF) or a high value in a quantified phase analysis (Phase SD) were found to have frequent ventricular arrhythmia and high Lown class. Significant correlations between LVEF or phase SD and the number of ventricular arrhythmias or Lown class were found (P less than 0.05). Frequent ventricular arrhythmias and high Lown class were also found in patients with inverse left ventricular wall movement at RNA. Prolonged QTc was found in patients with frequent ventricular arrhythmias. These connections were found at all three investigations during the follow-up year. A significant correlation was not observed between ventricular arrhythmias and exercise capacity, NYHA grouping, ST depression in an exercise test or symptoms of angina pectoris. More than 300 ventricular premature complexes (VPC) per 24 h was found to predict death during the follow-up year as was LVEF less than 30%; complex arrhythmia (i.e., the patient being in Lown classes 3-5) being the only factor to predict repeat-MI during the follow-up year. It is concluded, that ventricular arrhythmias in the post-MI patient reflect the left ventricular performance. Both LVEF and arrhythmias contribute univariately to the risk of death during the first year after an MI. Whether they both carry independent prognostic information for death must be studied in future larger trials.