Eighteen patients with acute transmural myocardial infarction were treated with intravenously administered heparin sodium to achieve the same standard of anticoagulation. Whole blood clotting times were obtained every two hours for the first 48 hours following hospitalization. Each of these patients had a second study during their second week of hospitalization. There was no consistent change in heparin requirement to achieve adequate anticoagulation immediately following admission and during the second week (ten days later). There was no demonstrable correlation between clotting time and heparin dosage once clinically adequate anticoagulant therapy had been achieved. Therapeutic benefits from anticoagulant therapy were not investigated in this study.