MAPK1 and cardiac hypertrophy: Both ERK1/2 activation by expression of a constitutive MEK1 transgene and ERK1/2 (Mapk1/Mapk3) double knock-out resulted in cardiac hypertrophy; however, the former results in a non-fibrotic concentric hypertrophy with thickened myocytes58, while the latter resulted in ventricular dilation and elongated myocytes36.