What is ischemia?

Ischemia refers to the condition where there is a lack of sufficient blood supply to an area of the myocardium, which is the muscular tissue of the heart. This inadequate blood flow typically occurs due to narrowed or blocked coronary arteries, leading to insufficient oxygen delivery to the heart muscle. The significance of ischemia lies in its potential to cause chest pain (angina) and can precipitate more serious conditions such as myocardial infarction (heart attack) if the blood supply is not restored promptly.

In contrast, excessive blood flow would imply a situation contrary to ischemia, where the heart muscle receives more blood than needed, which is not the definition of ischemia at all. An abnormal heart rhythm pertains to the electrical activity of the heart and does not directly define ischemia. Lastly, the complete blockage of a coronary artery is a more severe condition that may lead to ischemia but is not synonymous with it, as ischemia can occur with partial blockage or narrowing as well. Therefore, the correct answer accurately describes the fundamental nature of ischemia regarding blood supply to the heart.