Autosomal Emery–Dreifuss muscular dystrophy and related disorders with dilated cardiomyopathy and variable skeletal muscle involvement are caused by mutations in LMNA , which encodes A-type nuclear lamins. How alterations in A-type lamins, intermediate filament proteins of the nuclear envelope expressed in most differentiated somatic cells, cause cardiomyopathy is only poorly understood. We demonstrated previously abnormal activation of the extracellular signal-regulated kinase (ERK) branch of the mitogen-activated protein kinase (MAPK) signaling cascade in hearts of Lmna H222P ‘knock in’ mice, a model of autosomal Emery–Dreifuss muscular dystrophy. We therefore treated Lmna^H222P/H222P mice that develop cardiomyopathy with PD98059, an inhibitor of ERK activation. Systemic treatment of Lmna^H222P/H222P mice with PD98059 inhibited ERK phosphorylation and blocked the activation of downstream genes in heart. It also blocked increased expression of RNAs encoding natriuretic peptide precursors and proteins involved in sarcomere organization that occurred in placebo-treated mice. Histological analysis and echocardiography demonstrated that treatment with PD98059 delayed the development of left ventricular dilatation. PD98059-treated Lmna^H222P/H222P mice had normal cardiac ejection fractions assessed by echocardiography when placebo-treated mice had a 30% decrease. These results emphasize the role of ERK activation in the development of cardiomyopathy caused by LMNA mutations. They further provide proof of principle for ERK inhibition as a therapeutic option to prevent or delay heart failure in humans with Emery–Dreifuss muscular dystrophy and related disorders caused by mutations in LMNA .