Background: Mitral stenosis (MS), accounts for 25% of rheumatic heart disease. Systemic arterial embolization is serious, sometimes fatal, complication of MS. Around 20% of patients with rheumatic MS may encounter systemic embolism during course of disease. Case Report: A 24-year-old male with worsening dyspnea was diagnosed with moderate MS with mitral valve area (MVA) of 1.4 cm2 and atrial fibrillation (AF) six years back. He was advised warfarin to maintain INR between 2 to 3. He had visited outdoor department 2 months back after a lost to follow up. His INR was 1.2 suggesting inadequate warfarinization. His MS had progressed as echocardiogram revealed critical MS (MVA= 0.5 cm2). There was huge mobile, ping-pong thrombus inside left atrium which failed to embolize because of critical MS which turned out to be blessing in disguise for him. He was advised open mitral valvotomy. Conclusion: Effective anticoagulation is very important for patients with MS having AF.