['Left ventricular hypertrophy (LVH) displays significant gender-based differences. 17beta-estradiol (E2) plays an important role in this process because it can attenuate pressure overload hypertrophy via 2 distinct estrogen receptors (ERs): ERalpha and ERbeta. However, which ER is critically involved in the modulation of LVH is poorly understood. We therefore used ERalpha-deficient (ERalpha-/-) and ERbeta-deficient (ERbeta-/-) mice to analyze the respective ER-mediated effects.', 'Respective ER-deficient female mice were ovariectomized and were given E2 or placebo subcutaneously using 60-day release pellets. After 2 weeks, they underwent transverse aortic constriction (TAC) or sham operation. In ERalpha-/- animals, TAC led to a significant increase in ventricular mass compared with sham operation. E2 treatment reduced TAC induced cardiac hypertrophy significantly in wild-type (WT) and ERalpha-/- mice but not in ERbeta-/- mice. Biochemical analysis showed that E2 blocked the increased phosphorylation of p38-mitogen-activated protein kinase observed in TAC-treated ERalpha-/- mice. Moreover, E2 led to an increase of ventricular atrial natriuretic factor expression in WT and ERalpha-/- mice.'] Does estrogen receptor beta protect the murine heart against left ventricular hypertrophy?