Colossal left main to right atrium fistula ligation complicated by left circumflex STEMI.

Congenital left main (LM) coronary artery to right atrium fistulas with progression to aneurysm development are rare. Most patients remain asymptomatic, but for those with progressive symptoms, intervention is required. However, there are potential life-threatening complications associated with surgical intervention. We present a case of an extremely rare markedly aneurysmal LM to right atrial fistula treated with surgical ligation complicated by inferolateral ST-elevation myocardial infarction several days post-operatively treated successfully using mechanical aspiration thrombectomy, a stent-retriever, balloon angioplasty, and subsequent intravascular ultrasound-guided percutaneous coronary intervention with drug-eluting stent.