Presentation of hydatid disease is uncommon in children, and cardiac hydatid cyst is rare at any age. The authors discuss a pediatric patient with cardiac hydatid cyst in the posterior wall of the left ventricle. The cyst was diagnosed by two-dimensional echocardiography and by serology. A 3 month course of mebendazole therapy was only partially effective. The patient remains asymptomatic 2 years after diagnosis. HYDATID DISEASE is endemic in the Middle East. In a study from a surgical hospital in eastern Libya, the disease accounted for 0.89 percent of all hospital admissions. The echinococcus cyst grows very slowly and unless located in a critical anatomic site, it takes many years to evolve. Consequently, presentation in pediatric patients is distinctly uncommon. In an epidemiologic study from Benghazi, only 11.7 percent of patients were under 10 years old. Cardiac hydatid disease is rare at any age, accounting for less than 2 percent of all hydatid disease. Since the introduction of two-dimensional echocardiography, more cases are being diagnosed. All the reports in the recent literature are in adult patients. We report here, however, a cardiac hydatid cyst in the left ventricular wall in a child.