Cardiac muscle
The heart gets blood through the coronary arteries.  These are special blood vessels that carry blood only to the heart.  In order to do its job, the heart muscle needs a constant supply of blood and oxygen from the coronary arteries.  If these coronary arteries get blocked, blood flow to the heart muscle can stop.  Without blood flow, the heart muscle gets no oxygen.  If this lasts long enough, the part of the heart muscle which is not getting enough oxygen dies.  This is called a myocardial infarction, or a heart attack.