Twenty-four patients with acute myocardial infarction were divided into two groups according to left-ventricular filling pressure (LVFP): group I (n = 13) with LVFP less than 20 mm Hg, group II (n = 11) with LVFP greater than 20 mm HG. After infusion of 3 mg nitroglycerin in the first and 6 mg in the second hour there was a highly significant decrease in the filling pressure (from 15 to 9 mm Hg in group I, 28 to 16 mm Hg in group II). Mean arterila pressure fell in both groups by an average of 9 mm Hg. There were only slight changes in heart rate. Cardiac output fell from 4.4 to 3.9 1/min in group I, while it rose significantly (from 3.5 to 4.0 1/min) in group II from an initially markedly decreased level. In patients of group II the subjective symptoms improved with positive changes in the haemodynamic variables. Electrocardiographic precordial mapping indicated that nitromapping indicated that nitroglycerin at a dose of 3 mg/h diminished the zone of ischaemia, while at a dose of 6 mg/h S-T elevations and depressions increased again.