CASE PRESENTATION: A 31 years old male was brought to the emergency department by EMS for cardiac arrest after he collapsed in the field while running a marathon. As per EMS records, patient received about two minutes of cardiopulmonary resuscitation before he had a shockable rhythm and subsequent return to spontaneous circulation. In the emergency department (ED), he was intubated for acute respiratory failure. Patient's medical history was significant for only attention deficit hyperactivity disorder for which he was taking methylphenidate. Initial laboratory values were consistent with post cardiac arrest, viz. elevated troponins, hyperkalemia, mild acidosis, and mild leukocytosis. Initial electrocardiogram showed sinus tachycardia with borderline ST segment depressions and tall T-waves in the anterolateral leads. Chest X-ray was suggestive of mild pulmonary congestion. An echocardiogram done in the ED was near normal with a preserved ejection fraction of 50% with some hypokinetic apical lateral and basal inferior segments. On day 2, most of the lab values normalized with improvement of the EKG as well as the chest X-ray. The patient was extubated successfully on day 2. A work up was initiated for the etiology of the cardiac arrest, with initial suspicion for arrhythmogenic right ventricle dysplasia and abnormal coronary anatomy. A MRI of the heart was done which showed diffuse delayed enhancement of the left ventricle myocardium with inability to nullify the blood pool, suspicious for amyloid cardiomyopathy. A CT angiogram of the heart showed a 2-cm segment of myocardial bridging in the mid left anterior descending artery without any evidence of coronary artery disease. In view of these findings, the patient was scheduled for an abdominal fat pad biopsy, which showed yellow/green birefringence under polarized microscopy with a Congo red stain.