We examined the cardiovascular response at rest and during upright cycle exercise in nine women during pregnancy (25.6 +/- 3.0 weeks' gestation) and at 2 months (8.8 +/- 1.8 weeks) and 7 months (30.0 +/- 2.5 weeks) post partum. Antepartum resting cardiac output, heart rate, and stroke volume were higher, whereas the arterial-venous oxygen difference was lower than both postpartum values. The antepartum resting oxygen uptake did not differ from 2 months post partum but was higher than at 7 months post partum. Cardiac output during submaximal exercise was greater antepartum than at both postpartum tests. Submaximal antepartum oxygen uptake, heart rate, and stroke volume were generally higher, and the arterial-venous oxygen difference was lower than at 7 months post partum. The slope of the antepartum cardiac output versus oxygen uptake relationship did not differ from the value at 2 months post partum, (6.16 +/- 1.38 and 5.84 +/- 1.34, p greater than 0.05) but was higher than at 7 months post partum (5.22 +/- 0.78, p less than 0.05). There were no significant differences in maximal oxygen uptake or heart rate among the three testing periods. Maximal cardiac output and stroke volume were higher antepartum than at 2 and 7 months post partum, whereas the arterial-venous oxygen difference was lower than at 7 months post partum. There were few significant differences in resting, submaximal, or maximal measurements between the two postpartum conditions. These data suggest that the augmented cardiac response to exercise during pregnancy is reduced by 2 months post partum but that additional time may be required for a complete resolution of the cardiovascular changes induced by pregnancy.