In order to compare various physiological parameters under identical conditions and to evaluate the "optimal" combination of parameters for triggering a pacing system, a multisensor-catheter of 7 F size was developed. By this catheter placed in the right ventricular cavity, sinus rate (SR), mixed venous oxygen saturation (SO2), temperature (T) and stroke volume (SV) were continuously recorded in 7 volunteers. SR, T, SO2 and SV were analysed for their steady state relationships to workload (P) and for their dynamic characteristics during standardized exercise tests. During exercise the delay times of SR, SO2 and SV were less than 10 sec., whereas that of T was markedly longer ranging from 70 sec. at low exercise levels to 30 sec. at high levels (200 Watts). During recovery delay times of SR, SO2 and SV ranged from 5 to 10 sec., that of T ranged from 20 to 30 sec. The relationship of SR to the workload (0-200 W) performed was linear (r = 0.98), that of T was linear above 50 Watts (r = 0.92), that of SO2 followed an exponential function (r = 0.89). Initial changes of SV were independent (r = 0.02) of the extent of workload. The sensitivity (S = dV/dP) was calculated from the relationship of the parameters (V) measured to the level of exercise performed. SO2 was highly sensitive at the lower range of exercise (less than 75 W), T became constantly sensitive above 50 W, below 50 W the sensitivity of T was continuously decreasing. SR was constantly sensitive over the whole range of exercise (0-200 W), the initial change of SV was not sensitive to the extent of workload.