Background <p>Iatrogenic atrial-aortic perforation during transseptal puncture is a rare but potentially life-threatening complication. Percutaneous closure using dedicated occluder devices has emerged as a less invasive alternative to surgical repair in selected patients.</p> Case presentation <p>A 68-year-old woman with hypertension and long-standing persistent atrial fibrillation (≥ 12 years) underwent catheter ablation. Pre-procedural imaging showed a markedly elevated left atrial (LA) volume (171 mL) with predominantly lateral enlargement. During a second transseptal puncture attempt, the sheath-dilator system inadvertently advanced through the LA wall and perforated the sinotubular junction of the aorta, confirmed by aortography. Although the sheath initially tamponaded the perforation, subsequent migration led to rapid hemopericardium requiring cardiopulmonary resuscitation (CPR) and emergent pericardiocentesis. With the access tract preserved, a 12/10&#xa0;mm Amplatzer Duct Occluder was delivered percutaneously, achieving successful closure. Following device deployment, sudden cardiac arrest occurred due to diffuse coronary vasospasm, which resolved rapidly with intracoronary nitroglycerin. The patient was discharged in stable condition on an oral anticoagulant, a calcium channel blocker, and long-term nitrates.</p> Conclusions <p>This case describes the successful percutaneous management of an iatrogenic LA-to-ascending aorta perforation during transseptal catheterization, complicated by cardiac tamponade and coronary vasospasm. This case suggests that careful attention is warranted not only during the septal puncture itself, but also during subsequent sheath advancement, even after successful entry into the LA has been confirmed.</p>