This study examined the relationship of oxygen pulse (O2pulse) to stroke volume (SV) and arterio-venous oxygen difference [diff] during submaximal cycle exercise in untrained (UG) and trained (TG) males. Fourteen volunteers in each group completed an incrementalmax test and a submaximal test at 60%max to determine cardiac output (Q) via CO2rebreathing., Q, and heart rate (HR) were used to calculate SV anddiff. There were no significant differences (p >.05) between the two groups for O2pulse, SV, anddiff during submaximal exercise. Stroke volume index (SVI) was significantly higher (p <.05) in the TG. O2pulse was significantly related to SV and SVI (p <.05) but not todiff in both groups. Regression equations for predicting SV from O2pulse for UG and TG wereY = 6.81X + 26.7,SE = 21.4,r = 0.84, andY = 10.33X - 32.3,SE = 14.2,r = 0.71, respectively. These results suggest that O2pulse can be used to predict SV during submaximal cycle exercise in untrained and trained men.Key words: cardiac performance, exercise, training status