MAPK3 and cardiac hypertrophy: In vitro studies have verified the positive effect of ERK1/2 on cardiac hypertrophy in cardiomyocytes treated with endothelin‐1 or phenylephrine.45, 46 Nevertheless, ERK1/2 deletion in the heart failed to suppress hypertensive cardiac hypertrophy after 14 days of Ang II or phenylephrine infusion in mice.47 The possible explanation for this inconsistency might be that Ang II or phenylephrine infusion induces hypertensive cardiac hypertrophy through other signaling pathways such as p38 MAPK and JNK1/2 in mice with ERK1/2 deletion in the heart.