Data were analyzed from 698 patients with proved acute myocardial infarction (AMI) to develop a method to predict the occurrence of complete heart block (CHB). The presence of electrocardiographic abnormalities of atrioventricular or intraventricular conduction during hospitalization was determined for each patient. The electrocardiographic risk factors considered were: first-degree atrioventricular block, Mobitz type I atrioventricular block, Mobitz type II atrioventricular block, left anterior hemiblock, left posterior hemiblock, right bundle branch block and left bundle branch block. A CHB risk score was developed that consisted of the sum of each patient's individual risk factors. CHB risk scores of 0, 1, 2 or 3 or more were associated with incidences of CHB of 1.2, 7.8, 25.0 and 36.4%, respectively. When applied to an independent AMI data base, as well as to the summed results of 6 previously reported series that identified predictors of CHB during AMI, a similar incremental risk of CHB as predicted by the risk score method was demonstrated.