OBJECTIVE: To determine the after-effects on sympathetic nerve activity and calf and systemic haemodynamics of symptom-limited exercise in young patients with dilated cardiomyopathy. PATIENTS: 14 young patients with dilated cardiomyopathy (mean (SEM) age 35 (2) yr) and 17 healthy controls (age 29 (2) yr). METHODS: Blood pressure, muscle sympathetic nerve activity, calf blood flow, plasma noradrenaline, and stroke volume were recorded during baseline rest and an hour after symptom-limited treadmill exercise (up to 45 min) at 70% of resting heart rate reserve. RESULTS: Before exercise, sympathetic nerve activity (45 (6) v 21 (2) bursts.min-1; P = 0.001) and calf vascular resistance (55 (5) v 31 (3) units; P < 0.0005) were higher in the dilated cardiomyopathy group, and there was a significant correlation between these two variables (r = +0.64; P < 0.001). Patients with ventricular dysfunction exercised for 31 (3) min. In both groups there were significant and similar reductions in diastolic blood pressure, total peripheral resistance, and calf vascular resistance after exercise. Sympathetic nerve activity and plasma noradrenaline were unchanged and there was no longer any relation between muscle sympathetic nerve activity and calf vascular resistance. Cardiac output increased in both groups but, in contrast to healthy controls, mean values for systolic blood pressure and stroke volume (P < 0.005) did not decrease in the cardiomyopathy group. For similar reductions in total peripheral resistance, there were two to three fold greater increases in stroke volume after exercise in patients with left ventricular dysfunction (P < 0.03). There was no relation between exercise duration and the magnitude of these after-effects of exercise in these patients. CONCLUSIONS: In young patients with dilated cardiomyopathy the haemodynamic after-effects of submaximal symptom-limited exercise resemble responses to pharmacological afterload reduction but are not accompanied by reflex sympathetic activation. Sustained calf and systemic vasodilation after exercise were not attenuated, as compared with healthy controls. These cardiac, peripheral, and sympathoneural after-effects provide further support for exercise training as a non-pharmacological adjunct to the management of chronic stable heart failure.