Abstract Body (Do not enter title and authors here): Background
Sarcoidosis, a systemic granulomatous inflammatory disorder can involve various organs, including the heart but isolated bi-atrial cardiac involvement is rare. Advanced cardiac imaging especially in atypical presentations, can aid in early diagnosis.

Case
A 59 year-old man with history of biopsy-proven pulmonary sarcoidosis presented with non exertional chest pain for 2 months. EKG, cardiac enzymes, and Initial echocardiogram(TTE) was unremarkable. Stress echocardiogram ruled out myocardial ischemia. CT scan noted mediastinal lymphadenopathy consistent with known sarcidosis. In absence of other explainable etiolgies for chest pain, Cardiac MRI was done and showed preserved biventricular function, subepicardial enhancement in the basal inferior, inferolateral, and anterolateral walls. The enhancement raised suspicion for CS. However, symptoms resolved spontaneously, cardiac workup paused and he was monitored conservatively with serial Echocardiogram(TTE) until onset of dyspnea 3 years later. Repeat TTE and EKG then noted newly enlarged left atrium and atrial tachycardia. Further testing with Cardiac positron emission tomographic imaging with F-18 fluorodeoxyglucose (FDG-PET CT) showed abnormal myocardial uptake in both atrial posterior walls but no ventricular involvement, indicative of isolated bi-atrial inflammation in CS. He was treated with prednisone and methotrexate. Successful symptom and inflammation resolution on FDG-PET CT occurred in 3 months

Discussion
CS is rare and seen clinically in about 5% and diagnosed postmortem in 25% of sarcoidosis cases. Symptoms vary widely, with potential for severe heart complications. Left ventricle and interventricular septum are commonly involved, but isolated bi-atrial involvement is rare. Early diagnosis aided by Cardiac MRI and FDG-PET CT is crucial. Prednisone is mainstay of treatment, often combined with methotrexate. Cases of concurrent atrial CS involvement and bi-atrial fibrosis with Left ventricular hyperenhancement are documented, but this is the first known report of isolated bi-atrial hyperenhancement on FDG-PET CT for CS. This case highlights the need for symptom correlation with clinical and imaging follow-up, especially in atypical presentations.