The aim of the study was to evaluate the responses to autonomic function tests during the healing period of myocardial infarction (AMI). In 24 patients, at 2 and 6 weeks after the acute event, Valsalva manoeuvre, deep breathing at 6 breaths per min, isometric handgrip and cold pressor tests were performed. Responses of arterial blood pressure (BP) and heart rate (HR) were measured. At 2 weeks post AMI a significant decrease in parasympathetic tone was noted: HR reduction during deep breathing: 18.5 +/- 5.7 beats.min-1 for controls vs 9.7 +/- 2.6 beats.min-1 for AMI, P < 0.001. Systolic BP response to handgrip and cold pressor test was only slightly (non significantly) increased: 30.6 +/- 12.9 mmHg (controls) vs 40.0 +/- 20.5 mmHg (AMI) for the handgrip test and 13.8 +/- 8.1 mmHg vs 18.0 +/- 10.1 mmHg respectively for the cold pressor test. At 6 weeks post AMI, the response to the deep breathing test (15.9 +/- 5.6 beats.min-1) no longer significantly differed from that in controls. In contrast, the sympathetic stressor tests showed a significant increase in systolic BP response: 63.8 +/- 21.9 mmHg, P < 0.001 and 26.1 +/- 14.9 mmHg, P < 0.05, respectively for the handgrip and cold pressor tests. It appeared that infarct localization had no effect on autonomic function tests. There is evidence of autonomic imbalance both at 2 and 6 weeks after AMI, with a rapid but transient decrease in vagal activity and enhancement of orthosympathetic nervous tone; this was markedly more pronounced at 6 weeks post AMI despite treatment with beta-blocking agents in all patients.