What does borderline heart blockage mean?

Coronary artery dz: When we say heart blockage we generally are referring the coronary arteries which supply blood to the muscle of the heart. When these close off, it usually results in a heart attack. Mild blockages would mean there is some narrowing of the vessel but not enough to cause any flow problems. Borderline is not a specific medical term, but probably means that it beginning to be enough to watch.