A nomogram for the adjustment of heparin dosage was developed to standardize heparin therapy and to reduce delays in achieving and maintaining a therapeutic activated partial thromboplastin time (APTT) result. Fifty consecutive patients with acute venous thromboembolism had their continuous intravenous heparin therapy adjusted according to this heparin nomogram. The effect of the nomogram on heparin therapy in these patients was compared with data from 53 historical control patients. The proportion of patients in the nomogram group who reached a therapeutic APTT at 24 hours after the start of heparin therapy was 66%, which increased to 81% at 48 hours. In contrast, 37% and 58% of the control patients reached a therapeutic APTT at 24 and 48 hours, respectively. The percentage of therapeutic APTT results of the total number of APTT determinations was greater in the nomogram patients than controls. The use of this heparin nomogram resulted in (1) achieving a therapeutic APTT at 24 and 48 hours in a large proportion of patients and (2) reduced periods of inadequate anticoagulation and overanticoagulation during heparin therapy.