The incidence and prevention of systemic embolism in patients with chronic left ventricular aneurysm have been controversial. This retrospective study investigated the incidence of clinically evident embolic events and the effect of oral anticoagulation in patients with unequivocal angiographically defined left ventricular aneurysm. Between 1971 and 1979, 76 patients met the ventriculographic criteria and received initial medical management. The median interval from myocardial infarction to ventriculography was 11 months (range 1 month to 16 years) and subsequent median follow-up time was 5 years. Twenty patients receiving anticoagulant therapy were followed up for a total of 40 patient-years and 69 patients not on anticoagulant therapy were followed up for a total of 288 patient-years; 13 patients were included in both subsets. Twenty-eight patients died during follow-up and the 3 and 5 year survival rates were 75 and 61%, respectively. Only one patient not receiving anticoagulant therapy had a clinical embolic event, resulting in an incidence of 0.35 per 100 patient-years. Therefore, in the absence of other predisposing conditions, the extremely low incidence of systemic emboli in these patients with chronic (first documented at least 1 month after myocardial infarction) left ventricular aneurysm does not justify the use of long-term oral anticoagulant therapy.