Over a 2-year period, 450 cases of acute myocardial infarction were treated in a coronary care unit. Arterial PO2 and PCO2, were routinely determined on the day of admission. In this retrospective study, the patients were divided into groups according to their PaO2 and PaCO2 and the incidence of various clinical findings. Patients with low PaCO2 and patients with low PaCO2 values displayed the highest CCU and hospital mortality. Hypotension-shock and frank pulmonary edema were frequent in these patients. Pulmonary edema also was associated with high PaCO2 values, but left heart failure without pulmonary edema was only correlated to low PaO2 values. Supraventricular tachycardia, atrial flutter and fibrillation and left bundle branch block (including hemiblock) were common among patients with low PaO2 and PaCO2 values. Ventricular fibrillation was correlated to low PaO2and high PaCO2 values. The maximum respiratory rate recorded during the first day after admission proved an important indicator of short-term prognosis.