A 50-year-old man with diabetes and hypertension was admitted with a right-sided ischaemic stroke. Two years ago, he had undergone a single-chamber permanent pacemaker implantation for complete heart block. On admission, colour Doppler echocardiogram showed a possible hydatid cyst within the interventricular septum (IVS).

A 64-multislice contrast-enhanced CT scan revealed a multilocular hydatid cyst of size 4.7–5.5 cm in the IVS. This cyst (panels A and B) had daughter cysts and a clear fibrovascular wall. Hydatid cysts may be seen in the liver, lung, bone, brain and other tissues. They may remain silent for decades before presenting with pressure symptoms.

Sudden rupture can lead to anaphylaxis and death. Gradual leakage of intracystic contents produces allergic manifestations. Currently, this patient has refused any form of intervention. The heart block might have resulted possibly because of the cyst.