One hundred fifty patients underwent radionuclide left ventricular performance studies before and one week after resection of a left ventricular aneurysm. The patients were classified according to pre-and postoperative ejection fraction into five classes as follows: Class I > 50%, Class II = 41%-50%, Class III = 31%-40%, Class IV = 21%-30%, and Class V = < 21%. They were also classified into groups according to the size of the aneurysm and wall thickness. Operative mortality was 4.6% (7/150). One hundred one patients (67%) improved at least one "ejection-fraction class" postoperatively; whereas in a similar group of patients who underwent aortocoronary bypass without left ventricular aneurysm resection, only 42.3% (58/137) improved (p <.01). Preoperatively, ejection fraction was < 40% in 136 patients (90.6%); and postoperatively, it was > 40% in 59 patients (39.3%) (p <.01). Improvement of at least one "ejection-fraction class" occurred in 22 patients (47.8%) with small aneurysms, 54 patients (69.2%) with moderate size aneurysms (p <.05), and 25 patients (96.1%) with large aneurysms (p <.01). Sixty-nine patients (88.4%) with thin-walled aneurysms and 32 patients (44.4%) with thick-walled aneurysms improved (p <.01). Resection of a left ventricular aneurysm improves left ventricular function, particularly in patients with large, thin-walled aneurysms. A less aggressive surgical approach is warranted when dealing with thick-walled akinetic areas as patients with these lesions do not respond well to resection.