Inhibition of MEK suppressed the development of hypertrophy in WT mice, as assessed by echocardiographic measurement of the wall thicknesses of the interventricular septum at end-diastole (IVSd) and the LV posterior wall at end-diastole (LVPWd), heart weight normalized by tibia length, and individual cardiomyocyte size, after 1 week of TAC (Supplementary Fig. 2e–h). This evidence concerns the gene MAP2K7 and persistent truncus arteriosus.