We examined whether or not subsets of patients with complex ventricular arrhythmias after myocardial infarction are at high risk with respect to 1 year mortality after hospital discharge. Based on previous studies showing increased risk for those with non-Q wave infarcts, we hypothesized that complex PVCs (premature ventricular complexes) in this group might be associated with a poorer prognosis than complex PVCs in patients with Q wave infarcts. Seven hundred seventy-seven patients entering our study with acute infarction were followed prospectively for 1 year after undergoing a predischarge 24 hr ambulatory electrocardiographic examination. Patients were classified by electrocardiographic criteria into the following groups: Non-Q wave (n = 191), Q wave anterior (n = 261), and Q wave inferior infarction (n = 325). The following arrhythmias were classified as complex: multiform PVCs, couplets, and ventricular tachycardia. Sixty-two percent of patients with non-Q wave infarcts who did not survive 1 year had complex PVCs, compared with 32% of survivors (p less than .01). No differences were seen in the Q wave subgroup. The survival for patients with Q wave and non-Q wave infarction without complex PVCs were nearly identical at 1 year (93% and 90%), whereas in patients with complex PVCs survival for those with Q wave and non-Q wave infarction was 92% and 76%, respectively (p less than .001). Of those with non-Q wave infarction, only 4% of nonsurvivors were free of any PVCs, as compared with 28% of nonsurvivors in the Q wave group (p less than .02).(ABSTRACT TRUNCATED AT 250 WORDS)