A-K) Section in situ hybridization showing expression of Bmp10 (A, E, I), Irx2 (B, F, J), Dkk3 (C, G, K) in E14.5 embryonic hearts, and X-gal-stained bisected P56 Control (D), Hand1LV-Cre;Hand1fx/fx;Hand2fx/fx (H), and Hand1LV-Cre;Hand1fx/fx;Hand2fx/fx;R26RDTA-rescued hearts (L). Note that the RV of the heart in panel L has been mechanically damaged. (M, N) Echocardiographic analyses of P56 mice revealed restoration of ejection fraction (M) and fractional shortening (N) in Hand1LV-Cre(+);Hand1fx/fx;Hand2fx/fx;R26RDTA mice (n = 15) compared to Hand1LV-Cre(+);Hand1fx/fx;Hand2fx/fx CKOs. Hand1LV-Cre(-);R26RDTA mice, denoted as DTA(+), are included as controls. Data are represented as mean ± standard error of mean.