心肌梗塞（Myocardial infarction简称MI、Acute myocardial infarction简称AMI），是一种急性及严重的心脏状态，其症状是不同程度的胸痛不适，也可能伴随着虚弱、发汗、晕眩、呕吐、呼吸困难、心悸、心跳不稳定，有时丧失知觉。其成因是部分心肌的血液循环突然全部中断，心肌因无法得到足够氧气而导致的损伤。一般是因为供应血液到心脏的冠状血管因白血球或脂质造成的易损斑块而堵塞。心肌梗死一般是有生命危险的医学紧急状态，它需要立刻采取急救措施。许多的心肌梗死发生于凌晨时段（0时到6时）。

Myocardial infarction (MI) or acute myocardial infarction (AMI), commonly known as a heart attack, occurs when blood flow stops to a part of the heart causing damage to the heart muscle. The most common symptom is chest pain or discomfort which may travel into the shoulder, arm, back, neck, or jaw. Often it is in the center or left side of the chest and lasts for more than a few minutes. The discomfort may occasionally feel like heartburn. Other symptoms may include shortness of breath, nausea, feeling faint, a cold sweat, or feeling tired. About 30% of people have atypical symptoms, with women more likely than men to present atypically. Among those over 75 years old, about 5% have had an MI with little or no history of symptoms. An MI may cause heart failure, an irregular heartbeat, or cardiac arrest.