The purpose of the present study was to determine whether patients with acute myocardial infarction (AMI) in Killip class II or III are likely to benefit from catheterization and coronary revascularization performed within 30 days of AMI. The study population was drawn from 2 national surveys performed during 1996 and 1998 in 26 coronary care units operating in Israel. Our analysis included 3,113 patients with AMI who were divided into 2 groups according to their admission Killip class: 2,484 patients (80%) in Killip class I, of whom 1,408 (57%) underwent cardiac catheterization and 1,076 were treated noninvasively; and 629 patients in Killip class II or III, of whom 314 (50%) underwent cardiac catheterization and 315 were managed conservatively. Patients in Killip class II or III who were treated invasively had lower mortality rates than their counterparts who were treated noninvasively at 30 days: 7.6% versus 15.6%, respectively (adjusted odds ratio [OR] 0.52, 95% confidence interval [CI] 0.28 to 0.92), and thereafter from 30 days to 6 months, 4.3% versus 13.6%, respectively (OR 0.34, 95% CI 0.16 to 0.68). In Killip class I patients, an invasive versus noninvasive management was not associated with a better outcome at 30 days: 1.6% versus 3.2%, respectively (OR 0.58, 95% CI 0.32 to 1.05), but with similar mortality rates at 30 days to 6 months, 1.9% versus 2.0%, respectively (OR 1.46, 95% CI 0.79 to 2.74). Thus, the present study suggests that patients with AMI in Killip class II or III on admission may benefit from cardiac catheterization and revascularization performed within 30 days from admission, whereas patients with AMI in Killip class I are less likely to benefit from this approach.