Current systolic time interval techniques have limited clinical applicability since patient co-operation and attention to the carotid pulse and phonocardiogram transducers are required. Therefore only surface electrodes were used to monitor the electrocardiogram and electrical impedance cardiogram first derivative (dZ/dt) in the acquisition of the timing signals. dZ/dt motion artefacts were eliminated by computerised ensemble averaging, thus permitting uninterrupted data acquisition. We studied the continuous response of multistage treadmill exercise on 13 normal volunteers, since maximal distortion of noninvasive measurements occurs in dynamic exercise. The individual response trends were combined for 6 symbolic indices and each mean index had a high statistical significance (P less than 0.001). This new method surveys continuously ventricular performance with surface electrodes and therefore has the potential of monitoring the ventricular performance of critically ill patients.