Inotropic response to frequence. Effect of ovariectomy on the rate-isometric force development relationship from 0.25 to 3.0 Hz in isolated left ventricle papillary muscles from sham operation (Sham) and ovariectomized (Ovx) rats at 7, 15, 30 and 60 days after surgery. Force (g/g) values are expressed as mean ± S.E.M. *different from sham (P < 0.05) using two-way ANOVA and post hoc Tukey test. Number of animals used is indicated.