1. Ischemic heart disease is caused by decreased blood flow to the heart muscle and can lead to heart dysfunction or death. The main cause is coronary artery atherosclerosis which narrows the arteries and reduces oxygen to the heart. 2. The electrocardiogram (ECG) is an important diagnostic tool for ischemic heart disease, showing changes in the ST segment and T wave, especially in acute and chronic events. 3. Myocardial infarction occurs when a coronary artery is suddenly blocked by a blood clot, causing irreversible heart muscle cell damage or death. Pathological Q waves and ST segment elevation on ECG indicate heart muscle injury.