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Introduction: Lymphocytic Myocarditis (LM) is the infiltration of lymphocytes into the myocardium. Viral infections such as Parvovirus B19, Human Herpesvirus 6 or enteroviruses are the most common cause of LM. After infiltrating the myocardium, lymphocytes cause inflammation and myocyte damage with resultant fibrosis leading to heart failure. Diagnosis is made using endomyocardial biopsy. Standard heart failure treatment protocols are often used along with support of Extracorporeal Membrane Oxygenation (ECMO) and/or cardiac assist devices to maintain cardiopulmonary stability. While most cases resolve spontaneously, severe cases with refractory heart failure require transplant. Description: A 23-year-old man with no significant medical history presented to urgent care with worsening shortness of breath and fatigue that started 4 days prior. EKG showed an intraventricular conduction block. He was transferred to the hospital where labs showed ProBNP 1375 pg/ml, Troponin 3,830 ng/L, and no leukocytosis. Respiratory panel for Influenza A&B, RSV, and COVID-19 was negative. Initial cardiac echo demonstrated LVEF 53% with basal to mid-septal hypokinesis. On hospital day 2, endomyocardial biopsy was performed and demonstrated lymphocyte-mediated myocardial destruction with no giant cells or granulomas. Pulmonary artery catheterization (cardiac index of 1.68 ml/min/m2 and mixed venous saturation of 47%) and repeat cardiac echo indicated severe heart failure. The patient was placed on VA ECMO and a Left Ventricular Assist Device was inserted. Days 3-11 saw management of arrhythmias while awaiting organ availability. On day 12, the patient underwent orthotopic heart transplant and decannulation from ECMO. Cardiac echo measuring allograft function showed LVEF 65% and normal RV function. Following routine de-escalation of care, the patient was discharged. Discussion: This case highlights the essential features and management of LM, a relatively rare cause of severe heart failure. The clinical course discussed here demonstrates how rapidly LM can progress from the time of presentation, even in previously healthy individuals. Prompt management and diagnosis are required for optimal care. LM with refractory heart failure may require progression to complex management, device support, and ultimately transplantation.