Abstract Body (Do not enter title and authors here): A Japanese male in his 80s was admitted to our emergency department with chest pain. His prior history was syncope and ventricular tachycardia. Transthoracic echocardiography (TTE) revealed thickening of the basal part of the antero-septal wall and thinning of the basal part of the inferior wall. Coronary angiography (CAG), cardiac MRI and blood test revealed no specific abnormalities. The day before his emergency admission, he visited the cardiology outpatient department for a periodic examination of cardiac hypertrophy. ECG, chest X-ray, and TTE were unchanged from his prior examination. However, that night, he experienced chest pain and was transferred to our hospital. On arrival, his vital signs were critical, with a blood pressure of 70/59 mmHg. ECG indicated ST elevation in antero-lateral leads. TTE detected pericardial effusion, and contrast-enhanced CT identified two focal areas of non-enhancement in the myocardium and pericardial effusion without signs of aortic dissection. CAG revealed no significant stenosis or obstructive lesion. During coronary angiography, the patient deteriorated to asystole. Cardiopulmonary resuscitation and percutaneous pericardial drainage were initiated. Hemorrhagic pericardial effusion was aspirated. Immediate surgical hemostasis was undergone, revealing about 2 cm lacerations and hematoma in the anterior and inferior wall. After surgery, he complained of abdominal discomfort. Esophageal gastrointestinal endoscopy was undergone to investigate the abdominal discomfort, and he was diagnosed with early gastric cancer. Endoscopic submucosal dissection (ESD) was undergone, and histopathological examination revealed adenocarcinoma and eosinophilic amorphous materials deposited in the submucosal vessels. Congo red staining of the submucosal vessels revealed orange-red areas. A technetium-99m pyrophosphatase scintigraphy showed Grade 2 uptake in the heart. Transthyretin (TTR) staining was positive in the specimen from ESD, leading to a diagnosis of TTR amyloidosis. Genetic test for TTR was negative, which led to a diagnosis of wild-type TTR amyloidosis and tafamidis was started. In cases of acute pericardial effusion and/or cardiac rupture, it is imperative to consider cardiac amyloidosis as a potential etiology, in addition to myocardial infarction and aortic dissection, especially in patients with left ventricular wall thickening, neuropathy, or abnormal ECG, also known as “red flag”.