Clinical and hemodynamic data of 30 patients with left ventricular aneurysm (27 men, 3 women, mean age 54.9 years) were compared with those of 30 patients with previous myocardial infarction and segmental hypo- or akinesis (28 men, 2 women, mean age 51 years). In each group, 10 patients were affected by one-, two-, or three-vessel disease. A semiquantitative evaluation of collateral coronary circulation showed no significant differences between the two groups. Mean end-diastolic volume was higher in patients with left ventricular aneurysm (p less than .025, less than .05, and less than .001 in 1-, 2-, and 3-vessel disease, respectively) and ejection fraction was lower only in patients with one-, (p less than .001) and two- (p less than .05) vessel disease in comparison with patients without left ventricular aneurysm. No significant difference was evidenced in basal or isometric exercise end-diastolic pressure. The incidence of thrombosis detected by ventriculography was higher in patients with left ventricular aneurysm (33.3 vs. 6.6%). The mean duration of follow-up was 20.7 months in patients with left ventricular aneurysm and 20.6 in the control group. No significant difference was found either in mortality or in reinfarction rate as far as incidence and severity of angina. The incidence of congestive heart failure was more evident, but not significant in patients with left ventricular aneurysm. One embolic episode was present in one patient with aneurysm and intraventricular thrombosis. Left ventricular performance is influenced by an aneurysm when a limited coronary compromise is present (one- and two-vessel disease) while it is not affected in the case of a coexisting three-vessel disease.