A case of ventricular septal tumor diagnosed in 7-month-old boy is reported. An echocardiogram was performed for investigation of a heart murmur in an otherwise healthy infant. He remained asymptomatic, and the tumor had a very slow growth. When the boy was 9 years old, partial surgical excision was performed for right ventricular outflow tract obstruction. Histology showed a primary cardiac leiomyoma. To the authors’ knowledge, a primary cardiac leiomyoma of the ventricular septum has not been reported previously.