ObjectiveTo investgate the hemodynamic changes occurring in normal pregnanacy and to see if these changes were associated with an increase in myocardial contractility.MethodsIn a longitudinal study, primigravidas were studied with echocardiography in early (15 ± 1.8 weeks), mid (26 ± 1.2 weeks), and late (36 ± 1.0 week) gestation, as well as at 6 weeks postpartum. Carkiac dimensions were measured with two-dimensional and M-mode echocardiography and hemodynamic indices were calculated. All measurements were made with subjects in the left lateral decubitus position. Statistical analysis was performed with repeated measures analysis of variance.ResultsSeventy-six women with normal pregnancy outcomes completed all four studies. From the baseline study to late gestation, an increase in cardiac output of 27% (from [mean ± standard error] 4.2 ± 0.1 to 5.8 ± 0.2 L/min,P= .001). and a decrease in total peripheral resistance of 33% (from 1356 ± 69 to 941 ± 37 dynes/second cm−5,P= .001) occurred. Over this same time period, left ventricular function, while demonstrating a small and non-significant increase in velocity of circumferential fiber shortening (from 1.25 ± 0.02 to 1.27 ± 0.02 cm/second), revealed a 12% decrease in wall stress (from 36.3 ± 1.0 to 31.9 ± 1.0 g/cm2,P= .001) and a 13% decrease in the load-independent wall stress to velocity of circumferential fiber shortening ratio (from 30.0 ± 1.2 to 26.1 ± 1.0,P= .01), impluing enhanced intrinsic myocarial contractility.ConclusionNormal pregnancy is characterized by enhanced myocarial performance.