ABSTRACTHeart rate and central venous blood temperature (CVT) were measured in 31 people with different exercise capacities by means of a thermistor intergrated into a lead that was placed in the right ventricle. Bicycle ergometric and treadmill stress tests with increasing workloads were performed. The maximum increase in CVT with ergometric exercise was found to be 1.30 C at 250 W in healthy young volunteers and 1.00 C at 125 W in cardiac patients. Despite a relatively greater increase in CVT in the elderly patients compared with the volunteers, the correlation between the increase in CVT and that in heart rate at the end of each exercise stage was found to be very high (r = .9693 in volunteers and r = .9864 in cardiac patients), independent of physical fitness. Even with everyday activities such as walking there was a marked increase in CVT. Due to its close relationship to human metabolism, CVT represents a good parameter for physiologic control of pacing rate.