One hundred and one subjects (52 men, 49 women) with low probability coronary disease and normal resting left ventricular ejection fraction performed upright bicycle exercise to target without angina, ischemic ECG change, or segmental wall motion abnormality. Fifteen millicuries of Tc-99m pertechnetate were injected at rest and during peak exercise, and images were processed with first pass technique (RNA). The responses were not uniform. Group 1 was characterized by the resting end diastolic volume index (EDVI) usually greater than 80 ml/M2, a peripheral resistance drop (decreases R) of 0.20-0.50, an increase in cardiac index (increases CI) of 2.8-5.5 1/minute/M2, accompanied by decreasing EDVI and ESVI with exercise, stroke volume index (SVI) remaining essentially unchanged, and left ventricular ejection fraction (EF) usually increasing. Group 2 was characterized by the resting EDVI less than 80 ml/M2, and with the same decreases R and increases CI; EDVI, ESVI, SVI all increased and EF tended to decrease. Group 3 was characterized by decreases R greater than 0.50, increases CI greater than 5.5 1/minute M2, the exercise EDVI usually increasing, ESVI usually decreasing, SVI usually increasing, and EF usually increasing. There were no significant differences (alpha = 0.01) in exercise-related changes between men and women within each group.