Ischemia is a condition where blood flow and oxygen to tissues is restricted or reduced. It occurs when blood supply is blocked by a clot or embolism, or arteries are constricted. This can be caused by atherosclerosis, trauma, or other problems affecting blood vessels. Ischemia leads to a shortage of oxygen needed for cellular metabolism and function. Without oxygen, tissue can become damaged or dysfunctional. Examples of ischemia include reduced blood flow to the heart (cardiac ischemia), brain (ischemic stroke), feet, hands, and mouth.