Neurocutaneous syndromes are heterogenous diseases that are diagnosed in the presence of skin and central nervous system disorders. Neurofibromatosis (NF) is one of these disorders, with autosomal dominant inheritance, that causes tumors that grow on nerves as well as other abnormalities such as skin changes and bone deformities. The most common form of NF is type I. A 6-year-old Iranian boy with neurofibromatosis was referred to the pediatric cardiology clinic due to a soft holosystolic murmur discovered on routine examination. The echocardiographic findings included a large intrapericardial, encapsulated echodense homogenous mass located in the posterior part of the pericardium, attached to the posterior aspect of the left atrium and left ventricle. The mass measured about 6.3×6.5×5.5cm and exerted a compressive effect on the left-side chambers, with mild mitral regurgitation and mild pericardial effusion. Magnetic resonance imaging confirmed these findings showing encasement of the left circumflex artery, while the open biopsy through a midsternotomy procedure showed a mildly cellular mesenchymal tumor composed of spindle cells suggestive of neurofibroma. Further resection of the mass was not performed because of the risk of coronary injury and the stable situation of the patient. Visceral involvement of neurofibroma is uncommon and rarely involves the heart. As shown in this case, besides the chance for involving the pericardium, despite its benign nature, this tumor sometimes shows unusual involvement of structures such as the coronary arteries.