The authors investigated how a previous myocardial infarction (MI) affects the prognosis of unstable angina pectoris in patients with maintained or slightly reduced left ventricular performance. From January 1991 to August 1993, 131 patients hospitalized with the diagnosis of Braunwald's class II-III unstable angina and ejection fraction > 40% were included. The enrolled patients were divided into two groups: (1) group I: unstable angina with prior MI (n = 70, 49 men, 21 women, aged between fifty-one and eighty years, mean: 65.7 +/- 8.5 years, Braunwald's class III: 71.4%), (2) group II: unstable angina with previous infarction (n = 61, 31 men, 30 women, aged between forty-nine and eighty, mean: 66.3 +/- 7.9 years, Braunwald's class III: 83.6%). The follow-up varied between six and twenty-four months. The frequency of major cardiovascular events (deaths, MI, reinfarction, heart failure, and recurrent unstable angina) and the number of revascularization procedures (percutaneous transluminal coronary angioplasty [PTCA] and coronary artery bypass grafting [CABG]) established during follow-up were evaluated. Hospitalization was 10.1 +/- 2.9 days in group I and 8.6 +/- 2.6 days in group II (P < 0.01). The duration of the follow-up was comparable between the two groups. Based upon predischarge noninvasive evaluation, patients in both groups were selected to undergo coronary and ventricular angiography: 38 of 70 (55.7%) in group I and 39 of 61 (62.3%) in group II; among them, 52.9% in group I and 24.6% in group II (P < 0.05) were submitted to coronary revascularization, while the others received medical treatments: 33 of 70 in group I and 46 of 61 in group II (P < 0.05). In the subset of patients submitted to angiography, the severity of coronary disease did not differ between the groups, and group I showed a statistically lower ejection fraction than group II (P < 0.005). The frequency of major cardiovascular events demonstrated a mortality rate of 2.9% in group I and 1.6% in group II. Acute MI/reinfarction accounted for 2.9% of the cases in group I and 3.3% in group II. Heart failure was present in 2.9% of group I. Recurrence of unstable angina was diagnosed in 11.4% of group I and 6.5% of group II. CABG and PTCA were performed, respectively in 7.1% and 5.7% in group I and in 6.6% and 4.9% in group II. During follow-up 75.7% of patients in group I and 80.3% in group II were asymptomatic. No significant differences in the frequency of cardiovascular events were reported between the two groups. As result of more aggressive therapeutic approaches following the detection of residual ischemia in patients with prior infarction, the authors conclude that the prognosis of unstable angina in the group with previous infarction does not seem to differ from that of unstable angina in the absence of prior necrosis in patients whose left ventricular function is maintained or slightly decreased.