A 40-year-old male with Becker muscular dystrophy presented with severe mitral regurgitation and underwent mitral valve repair. Following the surgery, the patient became tachycardic, and developed a continuous high grade-fever and hyperbilirubinemia. The patient's condition worsened and we eventually tested his thyroid levels and discovered abnormally high thyroid levels. After diagnosing a severe thyroid storm, the patient was treated with oral administration of Lugol's iodine and thiamazole, as well as an intravenous steroid, which led to an immediate improvement of symptoms. The incidence of thyroid storm after open-heart surgery is extremely rare but highly life-threatening if unrecognized.