This study was to elucidate the physiological effects of dynamic apneas, as performed as a discipline in breath-hold diving for recreational or competitive purposes. Therefore, cardiovascular and respiratory effects of apneas with simultaneously initiated exercise were investigated in ten trained breath-hold divers. They performed maximum duration apneas with face immersion (26 degrees C) under rest and exercise (40 W, 80 W and 120 W) on a cycle ergometer in the laboratory. Apneic time, heart rate (HR), mean arterial pressure (MAP), arterial oxygen saturation and O2 (.VO2) and CO2 exchange were measured. All end-apnea heart rates were lower than corresponding control values. Higher workloads increased the initial rise in HR and delayed the onset of bradycardia. After an initial drop, MAP rose to 150% of control towards the end of apnea. Apneic .VO2 was reduced by 25% during exercise and by 40% during resting apneas compared to eupneic control values. It was concluded that magnitude and time course of diving bradycardia depend on work intensity. Higher workloads delay the onset and attenuate HR reduction, presumably due to increased sympathetic activity. It was also found that apnea with simultaneously initiated exercise has an O2 conserving effect compared to eupneic exercise. Although aimed to be a realistic approach to breath-hold diving, the study has certain methodological limitations in terms of body-immersion (hydrostatic pressure effects) and body-cooling effects due to conduction of the experiments in a laboratory set-up.