A 32-year-old woman with a past medical history of paroxysmal atrial fibrillation, long QT syndrome, and implantation of an automatic iimplantable cardioverter-defibrillator (AICD) following cardiac arrest presented with disabling symptoms of paroxysmal atrial fibrillation due to recurrent AICD shocks. Before curative ablation, transesophageal echocardiography was performed to assess for existing thrombi. This is a rare case of successful resolution with apixaban of a massive left atrial appendage thrombus due to non-rheumatic atrial fibrillation that was successfully treated with apixaban.