Fetal and early neonatal left and right ventricular cardiac geometry and left ventricular cardiac function were studied by M-mode technique in a cross-sectional study between 28 and 40 weeks of gestation (n = 227) and a longitudinal study from 24 h before until 48 h after delivery (n = 15). Antenatally both ventricles were geometrically uniform; there was a 3.2-3.4-fold increase in left ventricular volume and a nearly 3-fold increase in left ventricular stroke volume and cardiac output. During the early neonatal period the right ventricular transverse diameter reduced in size; there was a further 1.1-fold rise in left ventricular volume and a further 1.2-1.3-fold rise in the left ventricular stroke volume and cardiac output.