Fetal cardiac changes due to ductal constriction by maternal ingestion of nonsteroidal anti-inflammatory drugs were studied morphologically in near-term rats as an animal model, and results were compared with values of control 1 (Cl, twenty-first day) and control 2 (C2, twenty-second day). The fetal ductus was constricted (–-70percent;) (p<0.05) by maternal administration of 10 mg/kg indomethacin. Dilatation of the right ventricle and evidence of congestive heart failure including increased pericardial effusion (+200percent;) (p<0.05) and an increase in water content in the abdominal wall were present at 1,4, and 8 hours after drug administration. At 24 hours after drug administration, concentric right ventricular hypertrophy was shown by a diminished right ventricular cavity (–-36percent; vs. C2) (p<0.05), increased right ventricular wall thickness (+70percent; vs. C2) (p<0.05), and increased right ventricular mass (+31percent; vs. Cl) (p<0.05). Left ventricular dilatation was indicated by an increased cavity volume (+87percent; vs. C2) (p<0.05) and increased muscle mass (+29percent; vs. Cl [p<0.05] or +9percent; vs. C2 [p>0.05]). Both the wet and dry weights of the ventricles were increased. In conclusion, fetal ductal constriction caused right ventricular hypertrophy, diminished right ventricular cavity, and left ventricular dilatation and hypertrophy at 24 hours after drug administration in rats after initial congestive failure.