The effect of restricted vitamin A supply to the mother on the biochemical development of the heart in rats has been studied. The vitamin A status of female rats was varied by supplying low, medium and adequate amounts (6, 40, 100 micrograms retinol/day/kg body weight respectively) of vitamin A during pregnancy and suckling. The vitamin A status of the mother caused an alteration in the developmental pattern of fetal heart in parameters of tissue weight, DNA, RNA and protein contents and the biosynthesis of DNA and protein from [3H]-thymidine and [3H]-leucine respectively. A dose-dependent effect of vitamin A on the metabolism of DNA, RNA and protein was observed in the developing rat hearts. Hence, emphasis should be given to the adequate availability of vitamin A to dams for the normal growth and development of fetal organs.