(A) Female HCM mice, which have high endogenous levels of estrogen, were placed on a standard soy diet high in phytoestrogens. Cardiac growth was attenuated in these mice, and contractile function was preserved. (B) Male HCM mice, who have low endogenous levels of estrogen, consumed a standard soy diet high in phytoestrogens. Relative cardiac growth was augmented in these mice. A decrease in contractile function was also observed along with LV chamber dilation and wall thinning. The potential molecular and physiologic mechanisms underlying these events are shown. All HCM mice consuming a soy-free, casein diet were significantly heavier than those consuming the standard soy diet. However, the female HCM mice consuming a soy-free, casein diet (C) did not demonstrate a hypertrophic response whereas the male HCM mice did (D). In addition, the casein diet did not negatively impact contractile function in these mice.