OBJECTIVE: To investigate blood pressure (BP) and heart rate (HR) responses to an isometric exercise test in obese non diabetic patients and to correlate the results with vagal function and plasma insulin concentration. SUBJECTS: 63 obese patients, 36 of whom had abnormal cardiac parasympathetic control (PS ), and 35 healthy control subjects. METHODS: Analysis of HR variations during three standardized tests: deep-breathing, lying-to-standing and Valsalva. Isometric contraction (handgrip) for 5 min. RESULTS: In the PS obese patients, resting HR and body mass index (BMI) were signi®cantly higher than in the PS 7 subjects and there was a trend to higher plasma insulin concentrations. Age-matched comparison showed that during the handgrip test, the increase in HR at the ®rst minute was signi®cantly higher in the PS 7 obese patients than in the controls. The increase in BP was signi®cantly lower in the PS obese patients than in age-and-BMImatched PS 7 obese patients. CONCLUSION: These data suggest that 1) there is an increase in cardiac vagal tone in PS 7 obese patients, since the early increase in HR at 1 min of the handgrip test, results from the withdrawal of vagal tone; 2) BP response to an isometric contraction is impaired in PS obese patients due to a lower sympathetic activation; 3) high plasma insulin concentrations may also contribute to limiting the BP response; and 4) autonomic disorders may account for alterations in the haemodynamic changes during exercise.