2012年美國心臟學會及歐洲心臟學會之第三次心肌梗塞的共識重新定義中，將急性心肌梗塞定義為，臨床出現心肌缺氧同時並有心肌壞死之實證。其診斷需合乎五大項要件之一：1.心肌生化標記的升高及( 或) 降低，最好以cTn值作為依據；2.心臟死亡；3.與PCI 有關的心肌梗塞；4.與支架血栓有關的心肌梗塞；5. 與冠狀動脈繞道手術有關的心肌梗塞。重新定義其中最明顯的改變就是心肌鈣蛋白的診斷數據不再使用正常範圍來做界定，而是以參考值上限做為指標。臨床之心肌梗塞的通用分類更新為五大型：第1型：自發性心肌梗塞；第2型：血流供需失衡的缺氧引起之心肌梗塞；第3 型：導致死亡之心肌梗塞，但缺乏心肌生化標記之檢驗數據；第4a 型：與PCI 有關的心肌梗塞；第4b 型：與支架血栓有關的心肌梗塞；第5型：與CABG有關的心肌梗塞。在臨床研究追蹤心肌梗塞疾病的發展過程與預後，應該建立在共識而且通用的心肌梗塞定義與診斷之標準，與訂定檢測心肌生化標記之品質。

Myocardial infarction (MI) is a major cause of death and disability worldwide. A standardized case definition of MI is of special importance since it is a means to obtain reliable and comparable data for evaluation of the effectiveness of prevention and curative strategies in countries with widely varying health systems. The scientific implications of MI has been redefined previously in a consensus document in 2000 and 2007, and updated in August 2012. At the center of the third definition of myocardial infarction, is the detection of a rise and/or fall of cardiac biomarker values, with at least one of the values being elevated (> 99th percentile upper reference limit). The preferred cardiac biomarker of necrosis is cardiac troponin. In addition, at least one of the five following supportive criteria should be met: 1. symptoms of ischemia, 2. new (or presumably new) significant ST/T wave changes or left bundle-branch block, 3. development of pathological Q waves on ECG, 4. imaging evidence of new loss of viable myocardium or regional wall motion abnormality, and 5. identification of intracoronary thrombus by angiography or autopsy. The clinical classifications of MI are also redefined as: type 1: spontaneous MI; type 2: MI secondary to an ischemic imbalance; type 3: MI resulting in death when biomarker values are unavailable; type 4a: MI related to percutaneous coronary intervention; type 4b: MI related to stent thrombosis; type 5: MI related to coronary artery bypass grafting. The redefinition of MI for clinicians has important and immediate therapeutic implications.