(A) Hearts from 15-week-old mice display right ventricular dysmorphism with a shift to the base, rounded apex, and severe right atrial dilation when compared with Nkx2-5C/+ hearts. (B) Representative images from MRI show increased trabeculation or noncompaction of the left ventricle in Nkx2-5183M/+ with even stronger penetrance in Nkx2-5183P/+ hearts. (C) Mild left ventricular dysfunction associated with a high degree of right ventricular dysfunction. Control: n = 14; 183M: n = 10; 183P: n = 8. *P < 0.05; ****P < 0.0001, unpaired t test equal variance 2 tailed. RA, right atrium; LA, left atrium; RV, right ventricle; LV, left ventricle; LV-EF, left ventricular ejection fraction; RV-EF, right ventricular ejection fraction.