We assessed total body water (TBW) content and cardiac function in 25 normotensive (N) and 22 gestational hypertensive (GH) women matched for age, gestational age, and prepregnancy body mass index (BMI) during the third trimester of gestation. Patients underwent maternal echocardiography, bioelectrical impedance analysis (BIA), and hematocrit (Hct %) evaluation. The TBW:Hct ratio (water balance index, WBI) was calculated. Hct was significantly lower in N vs. GH women (31.9+/-2.2% vs. 36.2+/-2.5; p<0.001). There was no difference in TBW between the two groups. WBI was higher in N vs. GH women (1.35+/-0.20 l.kg(-1) x m(-2) vs. 1.19+/-0.18; p<0.001). N subjects showed a higher stroke volume than GH patients (78.0+/-9.7 ml vs. 67.9+/-10.2; p=0.001). Atrial function was higher in N vs. GH women (left atrial fractional area change 57.4+/-5.1% vs. 42.5+/-7.5; p<0.001). A correlation was found between stroke volume and WBI ( r=0.93, p<0.0001). Maternal cardiac function and WBI are strongly related and might help in understanding the mechanisms of adaptation in normal and hypertensive pregnancy.