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.