The clinical characteristics and long-term survival of 284 patients from the Coronary Artery Surgery Study (CASS) registry data base who had moderate to severe congestive heart failure symptoms and a left ventricular ejection fraction greater than or equal to 0.45 were studied. A control group consisting of registry patients with an ejection fraction greater than or equal to 0.45 who did not have heart failure was used for comparison. Patients who had heart failure were older and more likely to be female and to have a higher incidence of hypertension, diabetes and chronic lung disease than registry patients who did not have heart failure. As a group, patients with heart failure had more severe angina and were more likely to have had a prior myocardial infarction than were registry patients without heart failure. At 6 year follow-up, 82% of patients in the heart failure group survived compared with 91% of patients in the control group (p less than 0.0001). Multivariate analysis using the Cox proportional hazards model identified the following independent predictors of mortality: regional ventricular systolic dysfunction, number of diseased coronary arteries, advanced age, hypertension, lung disease, diabetes, increased left ventricular end-diastolic pressure and heart failure symptoms. Among patients with heart failure, the 6-year survival rate of those who had three-vessel coronary artery disease was 68% compared with 92% for the group without coronary artery disease. However, the 6-year survival rate for patients with heart failure who underwent surgical revascularization of diseased coronary arteries was not significantly improved compared with that of patients treated medically.(ABSTRACT TRUNCATED AT 250 WORDS)