Severe hypothyroidism in children is known to produce cardiac abnormalities such as asymmetric thickening or hypertrophy of the interventricular septum, smaller internal dimensions of the left ventricle, a smaller left ventricular outflow tract, and less systolic septal excursion. In this report, we present a 1.5-year-old boy who was admitted to our hospital because of growth retardation. According to the clinical and laboratory findings, congenital hypothyroidism, dilated cardiomyopathy (DCMP), atrioventricular complete heart block and secundum type atrial septal defect were diagnosed.