Twenty-one patients were treated during the acute stage of a myocardial infarction for failure of the left or right ventricle. The systematic use of varying rates of flow of intravenous trinitrin (between 0.6 and 4.8 mg/h) was designed to find out for each patient the optimal effect on the cardiac index. The fall in pulmonary capillary pressure, obtained within 10 to 15 minutes, is proportional to the flow rate of trinitrin, and reaches 48% of its original value at a perfusion rate of 4.8 mg/h. The lowering of systemic arterial pressure is also proportional to the flow rate, and reaches 13% at a flow of 4.8 mg/h. The cardiac index and systolic index were significantly improved at flow rates of 1.2 to 2.4 mg/h, and lowered the pulmonary capillary pressure to levels of 17.6 mm of mercury and 15.3 mm of mercury respectively. Trinitrin given intravenously is very well tolerated, but it often become less effective after 24 hours of treatment, which implies that haemodynamic measurements must be made several times a day, and the speed of infusion often increased. The improvement in immediate and late prognosis is discussed relative to the initial values and Weber's index of survival.