Abstract Disclosure: A. Mubashir: None. F. Sajid: None. M. Sattar: None. Myxedema Coma is a life-threatening complication of hypothyroidism and often presents with multi-organ failure. However, reversible cardiomyopathy and acute renal failure are rare. Here, we present a case of iatrogenic hypothyroidism leading to myxedema coma with reversible organ failure. Case Presentation: A 58-year-old male with a past medical history of iatrogenic hypothyroidism after total thyroidectomy for follicular thyroid cancer, noncompliant with levothyroxine for the past three years, was brought to the hospital due to worsening mental status, low energy, and cold extremities for three days. On admission, vital signs were within normal limits. Laboratory studies revealed Random Glucose 113 (74-200 mg/dl), Na 134 (135-149 mmol/l), TSH: 217 (0.39-4.08 MCIU/ml), Free T4 <0.25 (0.58-1.64 ng/dl), Free T3 1.01 (2.53-3.87 pg/ml), BUN 53.3 (7-21 mg/dl), Creatinine 4.9 (0.5-1.3mg/dl). Urinalysis was positive for protein of 300 mg/dl (negative). Urine studies showed hematuria, total protein/cr 3.18 (<0.10), with increased total protein of 60/24 hours (0-12 mg/dl), suggesting glomerular etiology. Additionally, Bence Jones protein and monoclonal band were negative, interpreted as mild glomerular proteinuria. FeNa >2%, Urine sodium of >40 (20-40mmol/l) suggest acute tubular necrosis. EKG showed normal sinus rhythm with low voltage. To rule out diastolic dysfunction, an echocardiogram was performed, which revealed depressed systolic function with an ejection fraction of 31-35% and a large pericardial effusion with echocardiographic features of tamponade. He also had global cardiomyopathy with akinesis, especially in the inferior segments. He was treated with IV levothyroxine. Repeat imaging in one month showed an increase in ejection fraction to 55% with moderate-sized pericardial effusion and no echocardiographic features of tamponade. Global cardiomyopathy had also resolved. However, left ventricular systolic function was borderline, with delayed diastolic expansion of the right ventricle. Repeat creatinine was 2mg/dl. The patient’s condition greatly improved, and he was discharged with follow-up with endocrinology, nephrology, and cardiology. Discussion: In the available literature, diastolic dysfunction is associated with severe hypothyroidism. However, reversible global cardiomyopathy with decreased systolic function is rare. The pathogenesis of this myopathy is not well understood. Similarly, known mechanisms of renal injury in hypothyroidism include renal hypoperfusion, rhabdomyolysis, decreased kidney-to-body weight ratio, truncated tubular mass, and altered glomerular architecture. While the need to perform a renal biopsy or the use of goal-directed therapy for dilated cardiomyopathy remains questionable in such cases, reversible complications of severe hypothyroidism should be investigated in patients with suspected myxedema. Presentation: 6/2/2024