AHA/ACC guidelines are no intervention with any occlusion less than 70%...usually does not present any SOB, chest pain, etc.. If there are symptoms (chest pain, etc), medication is the first option...medication can/will open (dilate) coronary arteries and relieve symptoms. If medication is not an option (does not relieve symptoms or not able to tolerate), then a stent implant. If the occlusion is not appropriate for a stent (too long, complex location, too many lesions or an emergency) then a bypass.
It is very unlikely and not probable to have a heart attack based on coronary occlusions. When it is a problem the reduction of blood/oxygen due to occlusions present symptoms of shortness of breath, chest pain, fatigue, etc., and that occurs (usually) before any heart failure....
There are other medical problems that produce the same symptoms of coronary occlusions. With other problems treated or ruled out, medication, lifestyle, diet, etc. should be effective.
arteries are actually a lot bigger than they really need to be, they have a good reserve to them. You can have a 50% blockage and not notice it. I believe guidelines state that
70% and above should be treated with surgery and anything less is not considered a
real life threat. 30% is not much but the concern is how quickly it will grow.
The blockage will not go away on its own and there are many people with blockages this
size that are unaware of the fact.