Isosorbide dinitrate (ISD) was administered before, during and after 178 operations performed on 127 patients with arterial occlusive disease. Its influence on postoperative myocardial infarction, heart failure and mortality was tested by comparison with 188 operations performed on 140 patients with hypertension and/or old myocardial infarction receiving no ISD prophylaxis. Risk of cardiac complications was similar in both groups. Mortality in the ISD-treated group was significantly lowered as compared with the control group and was about half of the overall mortality in patients with arterial occlusive disease operated on at our hospital over the past 10 years. This difference depended partly on the influence of ISD on cardiac complications. Post-operative myocardial infarction during ISD prophylaxis occurred in 0.6% of cases as compared with 3.7% in the control group (p less than 0.05), whilst the respective values for postoperative heart failure were 5.7% and 18.2% (p less than 0.001). Both complications are related to absolute or relative hypoxia during the post-operative stress period. ISD is effective by lowering cardiac preload and afterload and thereby diminishing myocardial oxygen demand. ISD is the drug of choice for surgical patients since it provides a steady and long-lasting effect after sublingual absorption. ISD prophylaxis during the perioperative period is indicated in cases with coronary artery disease and with increased cardiac preload or afterload.