Rheumatic mitral stenosis, atrial fibrillation, and marked left atrial remodeling create a strong substrate for intracardiac thrombosis and systemic embolism. We report a 67-year-old woman with a previous ischemic stroke who had not received long-term anticoagulation or cardiological follow-up and presented with progressive exertional dyspnea, lower-limb edema, and signs of right-sided heart failure. Electrocardiography showed atrial fibrillation. Transthoracic and transesophageal echocardiography demonstrated rheumatic mitral stenosis with a mitral valve area of 1.5 cm² and a mean transmitral gradient of 8 mmHg, massive left atrial enlargement, dense spontaneous echo contrast with sludge, and multiple thrombi; the largest measured 60 × 40 mm. Therapeutic anticoagulation was initiated. Because of symptomatic valvular disease and the extensive thrombus burden, the patient underwent mitral valve replacement with left atrial thrombectomy. An organized 60 × 40 mm thrombus was removed, and postoperative recovery was uneventful. This case illustrates that thromboembolic risk in rheumatic mitral stenosis may be driven as much by atrial fibrillation, atrial remodeling, and blood stasis as by the transmitral gradient itself, and highlights the central role of transesophageal echocardiography in defining thrombus burden and guiding treatment.