Cardiac hydatid cyst is an uncommon disease, especially in children. The interventricular septum region is the most frequent localization. The cysts usually involve other organs making the etiologic diagnosis easier. Our young patient presented a single hydatid cyst. The etiologic diagnosis was difficult due to the negativity of the serologic tests and there were no other organs affected. Surgical ablation of the cyst was performed and histopathological analysis achieved.