This double‐blinded, randomized, placebo‐controlled study investigates the benefit of ARRY‐371797 on change in 6‐minute walk distance at 12 weeks in 160 patients with symptomatic DCM caused by a LMNA gene mutation, which will be the first study involving genotype‐specific therapy. This evidence concerns the gene LMNA and familial dilated cardiomyopathy.