It is important to realize that a severe heart attack does not occur commonly because of an artery which is already more than 70% blocked. The heart attack occurs more frequently in the artery which is less than 60% blocked. This may be explained to some extent by the fact that there are many areas of the arteries which have less than 60% blockage compared to areas with more than 70% blockage.When a heart attack occurs, the affected artery gets 100% blocked. Many times even if the artery gets 100% blocked, it happens slowly enough so that there is chance to develop collateral circulation and hence there is no heart attack. Once the artery is already 100% blocked, there is no risk of heart attack happening from that artery. On a routine check up even if all the three arteries are severely blocked and the ejection fraction of the left ventricle is normal, mostly medical management with risk factor modification may be sufficient. The fact that the ejection fraction is normal in spite of blockages in arteries shows that there is sufficient collateral circulation available to the heart muscle. In other words, natural bypass may have already taken place.