Hcn4 R2R3-LacZ transgenic animals subjected to transverse aortic constriction (TAC) had 30% greater heart weight to body weight (HW/BW) ratios compared to sham-operated animals (A) and had induction of ANF expression as assessed by quantitative PCR on whole ventricle RNA (B). Whole-mount bluo-gal staining showed no expansion of enhancer activity beyond the AVB/LNC in the sham-operated animals (C,D), whereas animals subjected to TAC showed an increase in enhancer activity throughout the subendocardial myocardium of the left ventricle (lv) where pressure load is the greatest (D,E). By comparison, the right ventricle (rv), which is not pressure-loaded in this experiment, did not show any increase in enhancer activity. Each value 32 is expressed as mean with error bars denoting standard error of the mean. Means were compared with two-tailed t-tests (*, p<0.05; ***, p<0.001). Abreviations: ivs, interventricular septum; avb, atrioventricular bundle.