To determine if the postpartum period is reflective of a woman's cardiovascular status before pregnancy, we performed serial studies of 13 women before conception and at 6 and 12 weeks post partum. All pregnancies were singleton without hypertensive complications. Cardiac output, stroke volume, and end-diastolic volume were calculated with M-mode echocardiography from the left ventricular dimensions with subjects in the left lateral position. Systemic vascular resistance was calculated from cardiac output and simultaneous measurements of blood pressure. Stroke volume and end-diastolic volume remained consistently elevated over preconception values at 6 and 12 weeks. Systemic vascular resistance remained decreased, compared with baseline, at 12 weeks. Thus cardiovascular parameters had not returned to the preconception baseline, and previous studies that have used this time period for comparison have underestimated the contribution of stroke volume to the total change in cardiac output during pregnancy.