Restrictive cardiomyopathy (RCM) is characterized by impaired ventricular diastolic function with preserved ventricular contraction and wall thickness. The prognosis of young children with idiopathic RCM is poor, and the 2-year transplant-free survival rate has been reported to be approximately 40%. No medical treatment has been established for ventricular diastolic dysfunction; thus, heart transplantation is the only way to cure end-stage heart failure in patients with RCM. Herein, the pathology, etiology, clinical examinations, and medical management of pediatric patients with RCM were reviewed. This article includes a clinical case review of pediatric patients with RCM in our institute and the results of in vitro experiments using cardiac fibroblasts derived from patients with RCM and exome sequencing.