Delayed or late potentials after myocardial infarction is a marker of the risk of severe ventricular arrhythmias. We looked for the factors favorising the appearance of these potentials in 208 consecutive patients (172 men, 36 women) admitted to hospital for primary myocardial infarction. Coronary angiography, evaluation of the left ventricular ejection fraction and signal averaged electrocardiography were performed in all patients who were then divided into two groups (Group I: patients with delayed potentials; Group II: patients without delayed potentials). A multivariate analysis of 7 different clinical and paraclinical parameters possibly related to delayed potentials was undertaken. The overall incidence of delayed potentials was 20%. The coronary artery responsible for the infarct was occluded in 79% of patients in Group I and 31% of patients in Group II (p less than 0.00009). The left ventricular ejection fraction was significantly lower in Group I (45.9% vs 54.5%, p less than 0.0002). The incidence of anterior infarcts was 58% in Group I and 37% in Group II (p = 0.008). These 3 factors were independent and correlated with the presence of delayed potentials. The multivariate analysis showed that the major factor was coronary occlusion with presence of delayed potentials multiplied by 6.3, whereas anterior infarction multiplied the risk of delayed potentials by 2.6 and each 10% decrease in LV ejection fraction increased the risk by 1.4.