While it is established that the quality of the perinatal environment is critical in sculpting the developing individual, the mechanisms by which this occurs remain poorly defined. The growing fetus is dependent on the nutrients (including oxygen) it receives from the mother via the placenta. When this supply line is compromised, heart growth patterns are altered. In addition, hormones, other circulating factors, and the hemodynamic environment in which the fetus develops are important in determining outcomes for organ structure and function. Numerous studies in sheep have demonstrated that heart development can be modified in a number of ways, and the nature of the change differs between types and gestational timings of insults. Embolization of the placenta leads to the cessation of proliferation and maturation of cardiomyocytes; this may be due in part to changes in circulating insulin-like growth factor-1 levels. Such insults may be the underlying cause of cardiovascular disease in adults. Insults that modify the maturational timeline, final myocyte number, vascularity and endothelial responsiveness in the heart can have effects that persist long after the insult has been ameliorated.