Left atrial appendage aneurysm (LAAA) is a rare and often underdiagnosed cardiovascular anomaly with potentially serious complications, including arrhythmias and thromboembolic events. This report presents the case of a 36-year-old woman who developed LAAA after a recent viral respiratory infection. She presented with palpitations and atrial tachyarrhythmia, and transthoracic echocardiography (TTE) revealed a 5.6 x 3.5 cm aneurysmal left atrial appendage (LAA) with a reduced left ventricular ejection fraction of 50%. Cardiac computed tomography and cardiac magnetic resonance imaging confirmed the diagnosis, revealing a “smoky appearance” concerning blood flow dynamics and late gadolinium enhancement consistent with prior myocarditis. The patient successfully underwent minimally invasive endoscopic thoracoscopic aneurysm resection with cardiopulmonary bypass and transesophageal echocardiographic (TEE) guidance. No thrombus was found during preoperative TEE, and her postoperative recovery was smooth, with restored sinus rhythm, improved left ventricular function (55%), and no arrhythmias during follow-ups. This case highlights the crucial role of multimodal imaging, particularly echocardiography, in diagnosing and managing LAAA, while also drawing attention to a potential association with viral myocarditis. The successful use of minimally invasive surgical techniques underscores their value in optimizing outcomes for this rare condition, warranting further investigation to guide future practice.