Introduction: Cardiac fibroma is a rare benign tumor, although it is considered the second most frequent cardiac tumor in children. It is located in the ventricular myocardium, frequently in the interventricular septum. One third of the cases are asymptomatic, being discovered postmortem. Case presentation: A 10-year-old male child accused severe dyspnea a few minutes before its sudden death. Autopsy examination revealed hypertrophic cardiomegaly, the entire left ventricular wall being replaced by an enlarged tumor mass. On histopathological examination, the tumor was diagnosed as cardiac fibroma. Conclusions: Noninvasive examinations during childhood, such as cardiac ultrasound, increase the early detection of the tumors of the heart, decreasing the number of sudden death cases in young patients, especially children.