A specific subset of acute myocardial infarction was defined and named ‘the hypertensive-hyperkinetic-coronary-active’ subgroup. This subgroup included patients with acute myocardial infarction without pump failure or hypovolemia who continued to have hypertension and tachycardia, after relief of pain and who also had at least two recurrent ischemic episodes in the first days after a transmural event. Fifteen patients belonging to this group (group A) were studied in comparison with 15 other patients with acute myocardial infarction complicated by pump failure (group B). The alterations in hemodynamics, in circulating catecholamine levels and the clinical course during an intravenous infusion of isosorbide dinitrate were evaluated and the data obtained in the two groups were compared. The patients in group A had tachycardia, hypertension and upper normal filling pressures (pulmonary capillary wedge pressures: 15.8 ± 1.8 mm Hg). They had high levels of circulating catecholamines (1,343 ± 407 ng/l), a cardiac output of 5.9 ± 0.6 liters/min and stroke work index of 78 ± 11 (mean ± SD). The effect of intravenous nitrates on the left ventricular function curves of the two groups was the following: a marked shift downward and slight shift to the left in group A, as opposed to a moderate but significant shift upward and marked shift to the left in group B. The episodes of recurrent ischemia subsided in 13 out of 15 patients from group A. It appears therefore that the hyperkinetic patients with acute infarction are characterized by a hypersympathetic response, a typical hemodynamic profile and a particular response to nitrate therapy directionally opposite to the changes obtained in patients with acute infarction complicated with failure.