Abstract Body (Do not enter title and authors here): Introduction: Giant cell myocarditis (GCM), a rare and often fatal heart disease, presents diagnostic challenges due to its varied symptoms mimicking other cardiac conditions. Treatment can involve medical management and heart transplant. Early diagnosis and targeted therapy can improve survival without transplant.

Case presentation: A 66-year-old female with type II diabetes, obesity, and coronary artery disease (CAD), presented with dyspnea, orthopnea, epigastric pain, and hypotension. Laboratory findings showed troponin at 2301 ng/L and lactic acidosis, with nonspecific ST changes on EKG prompting treatment for acute coronary syndrome (ACS). She was started on dobutamine and admitted to the cardiac ICU for cardiogenic shock. An echocardiogram revealed left ventricular ejection fraction (LVEF) of 25% with diffuse hypokinesis. She underwent coronary angiography which showed no significant obstructive CAD. She remained in cardiogenic shock despite inotropic support, prompting placement of an Impella and endomyocardial biopsy. Pathology revealed diffuse interstitial giant cells and multifocal cardiomyocyte necrosis, consistent with GCM. She was treated with pulse-dose steroids, tacrolimus, and placed on the heart transplant list. After 14 days with Impella 5.5 support, her LVEF improved to 45%. She has since been managed with mycophenolate, prednisone, and guideline-directed medical therapy for heart failure.

Discussion: Without treatment, GCM has a median survival of 3 months. Early diagnosis is often challenging as symptoms can mimic acute coronary syndrome. Refractory cardiogenic shock with myocardial injury in the presence of benign coronary angiography should prompt an endomyocardial biopsy to investigate uncommon etiologies such as GCM. While treatment primarily involves immunosuppressive therapy and heart transplantation, not all patients are eligible candidates for transplant. In this case, mechanical support stabilized the patient's hemodynamics, allowing immunosuppression to reverse myocardial inflammation, potentially improving survival, and reducing the need for a transplant. We highlight the diagnostic challenges of GCM and the critical role of medical and mechanical therapy in improving outcomes.