Dilated cardiomyopathy (DCM) is characterized by left ventricular dilation, and is associated with systolic dysfunction and increased action potential duration. Approximately 50% of DCM cases are caused by inherited gene mutations with genetic and phenotypic heterogeneity. Next generation sequencing may be useful in screening unknown mutations in such cases.A family was identified with DCM, in which the affected family members developed heart failure, arrhythmia, and sudden death. Probands and 4 affected family members underwent whole exome sequencing (WES), bioinformatics methods, and gene annotation to identify potentially causative variants. The Sanger sequencing method was used to verify the candidate mutation.WES yielded 2,238,831 variations. KCNJ12 (p.Glu334del) was identified as a candidate mutation, and the heterozygous mutation was verified by Sanger sequencing.Our study emphasizes the application of WES in identifying causative mutations in DCM. This report is the first to describe the KCNJ12 gene as a cause of DCM in patients.