Hydatid disease is a parasitic disease with a high incidence in pastoral areas in Tibet. The heart is an uncommon location of echinococcosis and involvement of the interventricular septum is even rarer. This disease can remain asymptomatic for a long time, but may result in cardiac tamponade and sudden death. We report a 55-year-old woman who was diagnosed with a giant cardiac hydatid cyst involving the interventricular septum associated with complete right bundle branch block. However, owing to insufficient treatment, spontaneous rupture of the cardiac hydatid cyst occurred 6 months after diagnosis, which caused sudden death of the patient.