The present study assessed the prognostic value of hyperglycemia--a common feature in the early phase of acute myocardial infarction (AMI)--in 330 nondiabetic patients. Seventy-nine known diabetics and 10 (3%) unknown diabetics--diagnosed before discharge by stable glycosylated hemoglobin greater than 6.9% and by oral glucose tolerance testing--were excluded. Thirty-three (10%) patients died. The mortality rate was higher in women, in patients with anterior AMI, in older patients (greater than 65 years) and in the presence of heart failure. It was highest in patients with cardiogenic shock (24/36 vs 9/294; p less than 0.0001). Admission plasma glucose was significantly higher in nonsurvivors than in survivors (163 +/- 60 vs 114 +/- 36 mg/dl; p less than 0.0001). Mortality rate increased with increasing admission plasma glucose: 3% in normoglycemic patients (less than or equal to 120 mg/dl) versus 15% in patients with borderline plasma glucose (121 to 180 mg/dl) versus 43% in hyperglycemic patients (greater than 180 mg/dl) (p less than 0.0001). Multiple regression (stepwise) analysis identified cardiogenic shock, infarct site and age as the major determinants of mortality, while admission plasma glucose failed to reach full statistical significance (p = 0.067). Hyperglycemia was related to all 3 of these independent prognostic factors; when age and infarct site were accounted for, hyperglycemia was significantly associated with heart failure only and this association was characterized by a remarkable mortality rate. In nondiabetic patients with AMI, hyperglycemia is a correlate of heart failure and, therefore, an important factor of prognosis.