The objective of the study was to evaluate postnatal changes in left ventricular (LV) contractility in very low birth weight (VLBW) infants. An echocardiographic study comparing 18 VLBW infants without significant complications and 16 normal term infants was carried out at the Neonatal Intensive Care Unit in Akita University Medical Hospital, Japan. The echocardiographic examinations were performed within 6 hours of birth and on day 5. We obtained the relations between rate-corrected mean velocity of circumferential fiber shortening (mVcfc) and end-systolic wall stress (ESS), which were calculated from two-dimensional LV short-axis views to compensate for the distorted LV shape, and we compared these relations statistically. In both VLBW and term infants there were inverse linear correlations between mVcfc and ESS for each study period (p < 0.05). The regression line of VLBW infants had a lower y-intercept and a steeper slope than that of term infants at 6 hours of age but almost corresponded on day 5. It is concluded that the left ventricle of VLBW infants adapts to postnatal hemodynamic alterations with low contractility but operates with a contractile state similar to that of term infants on day 5.