What Happens During a Heart Attack? The heart muscle requires a constant supply of oxygen-rich blood to nourish it. The coronary arteries provide the heart with this critical blood supply. If you have coronary artery disease, those arteries become narrow and blood cannot flow as well as they should. Fatty matter, calcium, proteins, and inflammatory cells build up within the arteries to form plaques of different sizes. The plaque deposits are hard on the outside and soft and mushy on the inside. When the plaque is hard, the outer shell cracks (plaque rupture), platelets (disc-shaped particles in the blood that aid clotting) come to the area, and blood clots form around the plaque. If a blood clot totally blocks the artery, the heart muscle becomes “starved” for oxygen. Within a short time, death of heart muscle cells occurs, causing permanent damage. This is a heart attack. While it is unusual, a heart attack can also be caused by a spasm of a coronary artery. During a coronary spasm, the coronary arteries restrict or spasm on and off, reducing blood supply to the heart muscle (ischemia). It may occur at rest, and can even occur in people without significant coronary artery disease. Each coronary artery supplies blood to a region of heart muscle. The amount of damage to the heart muscle depends on the size of the area supplied by the blocked artery and the time between injury and treatment. Healing of the heart muscle begins soon after a heart attack and takes about eight weeks. Just like a skin wound, the heart’s wound heals and a scar will form in the damaged area. But, the new scar tissue does not contract. So, the heart’s pumping ability is lessened after a heart attack. The amount of lost pumping ability depends on the size and location of the scar.