Background: Cardiac rhabdomyoma, a benign smooth muscle hamartoma, is the commonest heart tumor encountered in children. Arrhythmias and conduction disorders have been described with these tumors,
although most electrocardiographic abnormalities will resolve over time, concomitant with the resolution of the tumor.
Case Report: The case of a child, diagnosed with cardiac rhabdomyomas in fetal life, is reported in whom the tumors regressed in size over a four-year period whilst displaying a spectrum of conduction disturbances. He finally developed potentially lethal complete heart block.
Conclusions: Cardiac rhabdomyomas may be asymptomatic, cause hemodynamic compromise, or be associated with rhythm disorders. In the presence of conduction disorders, close monitoring is required with
regular electrocardiograms to detect potential lethal conduction disorders.

Keywords: Arrhythmias, Cardiac - physiopathology, Bundle-Branch Block - physiopathology, Child, Preschool, Electrocardiography, Heart Block - physiopathology, Heart Conduction System - physiopathology, Heart Neoplasms - ultrasonography, Infant, Newborn, Pre-Excitation Syndromes - physiopathology, Pregnancy, Rhabdomyoma - ultrasonography, Ultrasonography, Prenatal