This study compared the time from the onset of symptoms to the peak of the creatine kinase-myocardial band (CK-MB) in 34 consecutive patients with acute myocardial infarction. Patients were separated into two groups: group 1 (n = 21) had diagnostic (greater than or equal to 0.1 mV) ST segment elevation on the initial ECG, and group 2 (n = 13) did not have diagnostic ST segment elevation on the initial ECG. In group 1 the time to the peak CK-MB was 16.2 +/- 50 hours vs 10.0 +/- 2.0 hours for group 2 (p = 0.0001). Peak CK-MB was 331 +/- 276 IU/L in group 1 vs 81 +/- 54 IU/L in group 2 (p less than 0.005). In group 1 there were 16 patients who subsequently had a Q wave myocardial infarction as opposed to one patient in group 2 (p = 0.0001). Patients who do not have diagnostic ST segment elevation on the initial ECG have an early but low peak of CK-MB and typically have a non-Q wave infarction. These findings are consistent with early spontaneous restoration of blood flow during the infarction process in these patients. This early restoration of blood flow may provide the substrate for the high incidence of recurrent ischemic events noted in patients with non-Q wave myocardial infarction.