Serum cardiac enzyme levels (CK, LDH, SCOT) were estimated and the ECG recorded for days following admission of 288 patients (Group I) to a stroke intensive care unit. Sixty-four of these patients, subsequently found not to have strokes, served as controls. Mean serum levels of all 3 cardiac enzymes were elevated in 8% of the 224 patients with stroke. The mean serum enzyme levels in patients with transient ischemic attacks (TIA) did not differ from controls. In a second group of 230 patients with stroke (Group II) serum CK levels were measured and the isoenzymes were fractionated to determine the tissue source of the enzymes. One hundred and one patients had raised total CK values and 25 of these (11≤) had raised CK-MB (heart) iso-enzyme, the remainder having CKMM (skeletal muscle) fraction. No serum CK-BB (brain) iso-enzyme was detected in any patient. Patients with positive serum levels of CK-MB had more evidence of acute myocardial ischemia on ECG (p ≤ 0.05), and more cardiac arrhythmias (p ≤ 0.001) than those with normal CK levels. Scattered areas of myocytolysis were found in the myocardium at autopsy in one patient. The acute rise in serum cardiac enzymes which we have recorded in the initial stages of stroke suggest that acute myocardial involvement is a commoner complication than is generally recognized. Also, since the CKMB rises were modest and progressive, it is more likely that this acute myocardial dysfunction is a consequence, rather than a cause, of the acute cerebrovascular lesion.