The authors report a case of rhabdomyoma of the right ventricular cavity with outlet obstruction in a three-months old infant. The diagnosis was established by echocardiography. Bidimensional echocardiography study showed a polypoid tumor of the right ventricle. During the systole it was projected through the pulmonary valve, obstructing part of it. The Doppler study showed an important gradient between the right ventricle and the pulmonary artery. The resection was performed with success. The diagnosis of cardiac rhabdomyoma was made by microscopic study. It is emphasized the importance of the echocardiographic study in an infant with oligosymptomatic cardiac murmurs.