We assessed forearm vascular and blood pressure responses to dynamic leg exercise in patients 7 and 28 days postmyocardial infarction. To determine a possible association between abnormal exercise vascular responses and baroreflex dysfunction, integrated and carotid baroreflex sensitivity and forearm vascular responses (during application of subhypotensive lower body negative pressure) were assessed. On day 7, 42 patients were compared with 21 age- and sex-matched controls. All subjects were assessed for (1) forearm vascular resistance during semierect exercise, (2) blood pressure measurements during erect treadmill exercise, and (3) integrated, cardiopulmonary, and carotid baroreceptor sensitivity. These studies were repeated in 13 patients on day 28. Forearm vascular resistance increased during exercise by 36% +/- 63% in patients versus 121% +/- 105% in controls (P = 0.0001), and fell in 15 patients, a response seen in none of the controls. Exercise hypotension was demonstrated in 5 patients, all of whom had abnormal vasodilator vascular responses. Those patients with vasodilator responses had a lower left ventricular ejection fraction (52% +/- 12% vs 62% +/- 9%; P = 0.007), and lower cardiopulmonary mechanoreceptor sensitivity (-6.6 +/- 3.9 units vs +6.4 +/- 10.4 units, P = 0.02) than those with constrictor responses, respectively. In the 13 patients studied on day 28, the change in forearm vascular resistance was similar to that observed on day 7 (36% +/- 63% vs 46% +/- 73%). Paradoxical vasodilation of forearm vessels during leg exercise is common in patients studied 7 and 28 days postmyocardial infarction, and is associated with lower left ventricular ejection fraction and abnormal vascular responses during subhypotensive lower body negative pressure.