A 61-year-old woman with a congenital double-chamber left ventricle (DCLV) was admitted because of an anterior ST-elevation myocardial infarction (STEMI). Urgent coronary angiography showed a thrombotic occlusion of the distal part of the left anterior descending artery (LAD). The left ventricular injection revealed a slightly reduced ejection fraction, antero-apical akinesia and an accessory chamber. Two dimensional and three dimensional echocardiography showed anterior akinesia with an accessory chamber at the apex which was separated by a fibromuscular ridge distal to the papillary muscles. The DCLV with myocardial contraction in the additional chamber was originally diagnosed seven years ago during a routine follow-up echocardiography in the course of management for thyroid cancer and at that time left ventricular function was described to be normal. Thromboembolism was assumed to have originated from the hypocontractile left accessory chamber and the patient was set on oral anticoagulation. During follow-up global left ventricular function normalized.