Many genetic diseases are caused by mutations in cis‐acting splicing signals, but few are triggered by defective trans‐acting splicing factors. Here we report that tissue‐specific ablation of the splicing factor SC35 in the heart causes dilated cardiomyopathy (DCM). Although SC35 was deleted early in cardiogenesis by using the MLC‐2v‐Cre transgenic mouse, heart development appeared largely unaffected, with the DCM phenotype developing 3–5 weeks after birth and the mutant animals having a normal life span. This nonlethal phenotype allowed the identification of downregulated genes by microarray, one of which was the cardiac‐specific ryanodine receptor 2. We showed that downregulation of this critical Ca²⁺ release channel preceded disease symptoms and that the mutant cardiomyocytes exhibited frequency‐dependent excitation–contraction coupling defects. The implication of SC35 in heart disease agrees with a recently documented link of SC35 expression to heart failure and interference of splicing regulation during infection by myocarditis‐causing viruses. These studies raise a new paradigm for the etiology of certain human heart diseases of genetic or environmental origin that may be triggered by dysfunction in RNA processing.