OBJECTIVE The aim of the study was to find out whether the presence of hypertension affects heart rate variability in patients rehabilitated after myocardial infarction. DESIGN Echocardiography, exercise testing and 24 h Holter monitoring were performed before and after 27 days of early postdischarge cardiac rehabilitation. PATIENTS The study population consisted of 64 patients aged 34-65 years (mean+/-SD 51.6+/-6.6) discharged from hospital after a first myocardial infarction who were subdivided into two groups, group A comprising 34 patients with arterial hypertension which had lasted 4.8+/-2.1 years and group B comprising 30 normotensives. MAIN OUTCOME We expected exercise rehabilitation to affect heart rate variability, exercise tolerance and myocardial ischemia in patients after myocardial infarction with and without arterial hypertension. RESULTS At baseline no intergroup differences were seen in the duration of exercise, workload and heart rate variability parameters. All parameters increased significantly after cardiac rehabilitation (P < 0.01): SD of all normal RR intervals 123.4+/-30.0 versus 123.8+/-30.0 ms; SD of the averages of normal RR intervals in all 5-min segments of the entire recording 115.1+/-30.5 versus 116.3+/-28.3 ms; mean of the SD of all normal RR intervals for all 5-min segments of the entire recording 49.0+/-12.5 versus 48.3+/-11.8 ms; square root of the mean of the sum of the squares of differences between adjacent RR intervals 29.7+/-9.1 versus 28.0+/-8.5 ms; percentage of differences between adjacent RR intervals > 50 ms 7.9+/-6.0 versus 7.1+/-6.1% (group A versus group B, respectively, NS). The duration of exercise and the workload were significantly increased (the rise was higher in normotensives). No differences were seen in the frequency and severity of silent myocardial ischemia. CONCLUSIONS Early stationary exercise rehabilitation after myocardial infarction improves heart rate variability parameters and exercise tolerance both in hypertensives and in normotensives.