Abstract Disclosure: D.J. Gomez D' Aza: None. T. Zahedi: None. F. Zhang: None. Introduction: Thyroid storm is an acute life-threatening complication of hyperthyroidism with high mortality rate. Plasmapheresis is often used in patients who are unresponsiveness to conventional treatment for thyroid storm. About 5% of thyroid storm patients present with heart failure while other cardiovascular dysfunctions include tachycardia, arrhythmias, hypertension, and pericardial disease. Myopericarditis is characterized by pericarditis associated with myocardial inflammation evident by elevated cardiac biomarkers. Thyrotoxicosis associated with pericarditis and myocarditis is rare. Here, we report a case of recurrent myopericarditis and thyroid storm in Grave’s disease treated with plasmapheresis. Case Report: A 47 years male with a history of Schizophrenia and Hyperthyroidism due to Grave’s disease was presented with poor oral intake, generalized weakness, and tachycardia with HR 180 bpm. Labs showed elevated troponin 0.505 ng/mL, Free T4 > 6.99 mg/dL, T3 > 651 ng/dL, and low TSH < 0.015 mg/dL. Burch-Warsofsky scale was 50 points which suggested thyroid storm. EKG revealed atrial fibrillation. Patient was managed with propranolol, propylthiouracil (PTU), iodine solution, hydrocortisone, and Diltiazem. However, his mental status deteriorated requiring intubation and patient developed cardiac shock with BP 77/53 mmHg. Troponin I trended up to 23.60 ng/mL and EKG showed ST-segment elevation in the anterior and inferior leads. Echocardiogram revealed severely reduced ejection fraction of 15 % and diffuse hypokinesis. Cardiac catheterization was unremarkable. PTU was discontinued due to liver dysfunction with AST and ALT levels above 1500 U/L and 2500 U/L. A session of plasmapheresis was initiated and the post labs showed an improvement of thyroid and liver function to Free T4 2.46 mg/dL, TSH 0.022 mg/dL, and ALT/AST 641/682 U/L. Patient was hemodynamically stable with normal sinus rhythm. Cardiac magnetic resonance images revealed left ventricular dilation with high T2 signal, late gadolinium enhancement in the pericardial region of basal inferolateral, inferior, and mid segments, consistent with pericarditis. Previous record showed patient had a similar admission 4 months ago with a diagnosis of myopericarditis. Discussion: The association of recurrent myopericarditis and hyperthyroidism may be related with the autoimmune dysfunction and underlying viral infection that precipitated inflammation of the thyroid gland, triggered thyroid storm, and caused cardiac event. Rapid correction of the hyperthyroid state is warranted in thyroid storm in addition to aggressive treatments for heart failure, arrhythmias, and myopericarditis. Our patient’s cardiac function improved rapidly after achieving euthyroidism by plasmapheresis. The treatment of hyperthyroidism is critical in preventing the recurrence of myopericarditis. Presentation: Friday, June 16, 2023