Hydatidosis remains an endemic disease in some regions of the world, such as Tunisia. The liver and the lungs are the most common sites in adults. Mediastinal and pericardial hydatid cysts are very rare even in endemic areas and true incidence has not been described in the literature. We report the case of a 74-year-old woman with clinical, biological and electrocardiographic features of acute myocardial infraction. Two-dimensional echocardiography and detailed imaging revealed a mediastinal and pericardial hydatid cyst. The particularity of the clinical presentation, the complementary investigations as well as the management and follow-up of the patient are discussed. This case is of great interest since the rarity of concomitant hydatid cyst in two uncommon localizations: mediastinum and pericardium, and the unusual incidental discovery during a myocardial infarction.