To compare echocardiograms of macrosomic and healthy full term neonates whose weight was appropriate for gestational age (AGA).Echocardiography was performed on 9 healthy full term AGA neonates and 15 macrosomic neonates. A data base was generated from valid echocardiographic measurements on each infant.Macrosomic infants were heavier than control infants and had a greater body surface area, but their mean cardiac dimensions were similar. The mean LVES volume was smaller than that of the control group when expressed as a fraction of individual LVED values (0.61 +/- 0.04 vs 0.64 +/- 0.02; p = 0.02). When comparing IVS/PW, it was observed that the ratio was up to and including 1.33 in the control group, while the upper limit of the ratio of the nondiabetic macrosomic infants was 1.6. The shortening fraction (SF%) was increased in comparison to infants of normal weight (40.67% +/- 3.34 vs 36.00% +/- 1.89; p = 0.0009). The thickened IVS did not elevate SF% by decreasing LVES; the macrosomic infants had a smaller LVES mean volume.IVS/PW ratio of macrosomic infants fell outside of the normal range. Macrosomic neonates were found to have an increased SF% secondary to a proportionally smaller LVES volume, regardless of IVS thickness.