Non-ST-elevation myocardial infarction (NSTEMI) has a less severe ratio of acute coronary syndromes compared with ST-segment elevation myocardial infarction (STEMI), arising from complete occlusion of a major coronary artery. The name implies a syndrome that does not exhibit the dramatic ST-elevation seen in the traditional 12-lead ECG in chest pain patients with a confirmed diagnosis of STEMI. The crucial clinical significance of NSTEMI is that delay in diagnosis can lead to increased morbidity, risk of arrhythmia, and death. It was recently reported that atrial fibrillation (AF) correlates with the risk rise of myocardial infarction (MI), although the mechanism underlying this association is currently unknown. Does atrial fibrillation with decompensated heart failure (DHF) get complicated with NSTEMI? In this article, we describe the case of a 77-year-old male patient diagnosed and admitted as NSTEMI complicated by DHF.