We next determined whether rutaecarpine influenced the ERK1/2 pathway in hypertrophic cardiomyocytes because the ERK1/2 pathway has been proved to play a critical role in pathological cardiac hypertrophy.26, 27, 28 The left ventricle of the AAC rats displayed increased activity of ERK1/2 compared with the Sham group, whereas low or high dosage of rutaecarpine remarkably decreased the phosphorylation level of ERK1/2 in the left ventricle of AAC‐induced hypertensive rats (Figure 6A). Here, MAPK3 is linked to cardiac hypertrophy.