A 3-year-old girl was diagnosed with restrictive cardiomyopathy (RCM) after showing symptoms of heart failure, and a 6-year-old boy was found to have RCM after abnormal electrocardiographic findings were seen during school-based heart disease screening. Both had typical clinical features of the disease. Plasma levels of brain natriuretic peptide increased significantly in both patients, allowing us to distinguish this disease from constrictive pericarditis which has similar clinical and hemodynamic features. The early diastolic mitral annular velocity recorded by tissue Doppler echocardiography was also useful to discriminate RCM from constrictive pericarditis. The former case successfully received heart transplantation, but the latter case died suddenly prior to receiving a heart transplant. The plasma level of brain natriuretic peptide and tissue Doppler echocardiography helped us to diagnose this disease earlier and follow it more carefully, which has important implications in optimal treatment and improved prognosis of RCM in children.