It is logical to say that the single most important factor in terms of prognosis from a heart attack is the size of the affected territory. The larger the territory that dies, the weaker the heart gets. The consequences of death of a large territory include death as a consequence of the heart attack or If the patient is lucky enough to survive the heart attack, a severely weakened heart and a lugubrious overall prognosis.

If areas within the heart were to receive blood from multiple arteries and therefore not dependant on a single blood artery then even if one vessel blocked off, the amount of damage would be minimised because cells within that territory would continue to receive blood from the other artery. Reassuringly, we now know that the coronary arteries are not isolated end vessels. They give off multiple smaller branches which in turn give off very tiny branches which connect to very tiny branches of the other coronary arteries so it is possible for the blood to get to areas of the heart supplied by an occluded vessel through the branches of another non occluded vessel. This is known as the coronary collateral circulation.