In this study we clarify the fetal cardiovascular effects of nifedipine. Nifedipine was administered to near-term rats and cardiovascular morphology of the fetus was studied with a rapid whole-body freezing technique. Fetal cardiac failure was estimated by accumulation of pericardial effusion and ventricular dilatation. Dose-response study at 8 h after administration revealed that slight ventricular dilatation occurred with 0.1 mg/kg of nifedipine, and remarkable ventricular dilatation and pericardial fluid accumulation were noted with 10 mg/kg nifedipine. Time-course study with one dose of 10 mg/kg nifedipine revealed early ventricular dilatation at 1 h, peak ventricular dilatation and fluid accumulation at 8 h, and slight effects at 24 h. In conclusion, the cardiodepressive effect of nifedipine in the fetal rat was mild with the therapeutic dose, and its effects increased dose dependently.