Introduction: Mucopolysaccharidosis (MPS) are lysosomal storage disorders characterized with the deficiency of enzymes involving in the destruction of glycosaminoglycans (GAG). Cardiac findings include cardiac valve thickening and dysfunction, conduction abnormalities, coronary artery and other vessels involvement. It is thought that GAGs, which are non-conductive electrically, causes failure in cardiac conduction. Arrhythmias are considered to be responsible from deaths of cardiac origin. In this study cardiac rhythm and structures were evaluated using Holter electrocardiography (ECG) and transthoracic echocardiography.