As a medical professional with expertise in cardiology, I can explain what an MI, or myocardial infarction (heart attack), looks like on an ECG (electrocardiogram). An ECG is a test that measures the electrical activity of the heart. When someone experiences an MI, the ECG can show characteristic changes that reflect the heart's response to the lack of oxygen caused by blocked coronary arteries. Here's what you might see: 1. ST-segment elevation: This is a hallmark of an MI. The ST segment represents the period between the end of the depolarization (ventricular contraction) and the beginning of the repolarization (ventricular relaxation). Elevation of the ST segment indicates that the heart muscle is experiencing ischemia (a lack of blood flow). 2. Q-wave changes: Q waves are the initial negative deflections of the ECG complex. In the context of an MI, new or significant Q waves may appear, which can be an indication of dead or damaged heart tissue. 3. T-wave inversion: T waves represent the repolarization phase of the ventricular myocardium. Inversion of the T wave can be seen in the leads corresponding to the area of the heart affected by the MI. 4. Pathological Q waves: These are wide and deep Q waves that can persist after the acute phase of an MI, indicating a large area of myocardial damage. 5. Changes in the QRS complex: The QRS complex represents ventricular depolarization. Changes in the QRS complex, such as widening or notched appearance, can also be indicative of an MI. It's important to note that the specific appearance of an MI on an ECG can vary depending on the location and extent of the heart attack, as well as the timing of the ECG in relation to the onset of symptoms. read more >>

These are the septal and anterior ECG leads. The MI is posterior (opposite to these leads anatomically), so there is ST depression instead of elevation. Turn the ECG upside down, and it would look like a STEMI. The ratio of the R wave to the S wave in leads V1 or V2 is greater than 1.read more >>