In case of severe stenosis and/or obstruction of coronary arteries, a balloon angioplasty is recommended, if applicable, at the same session or later. With balloon angioplasty, the narrowed section inside the vessel is enlarged by inflating the specially designed balloon for a short period of time. It is possible to use the same balloon for more than one stenosis of the same vessel, or for more than one vessel at the same session or different sessions. In addition to the balloon, a stent can be placed in the same area by means of balloon when required.
In the balloon procedure, a catheter with an inflatable balloon is inserted in the narrowed section (A) then the balloon is inflated to enlarge the stenosis (B).

Bypass surgery or pharmacotherapy is recommended when not possible to use balloon angioplasty.

In a bypass surgery, a graft is placed functioning as a bridge between the beginning and end sections of stenosis. This graft could be an artery from the saphenous vein or mammary vein of the patient. So, the blood is able to flow through the stenosis or obstructed section by means of that bridge.
This figure shows a LIMA to the left anterior descending (LAD) and saphenous bypass to the right coronary artery (RCA).

The medication used in coronary artery disease includes vasodilators, drugs to reduce work load of the heart, anticoagulants to prevent clots, or drugs to reduce cholesterol that have highly adverse effects on atherosclerosis. Such drugs should used at all times under doctor control.
This figure shows anastomosis of saphenous vein to the left anterior descending (LAD). First one end of the graft is stitched to the LAD then the other end is stitched to the aorta so that the blood from aorta can pass (bypassing) the obstructed section and flow smoothly to supply the heart.

Unfortunately, neither the drugs used to treat coronary artery disease nor balloon or bypass are able to remove vascular diseases. Thus, it is likely that new stenosis might occur in the same or a different location of coronary artery, or a mild stenosis might lead to a severe stenosis, resulting in various problems. It is therefore critical that patients remove the risk factors; take their drugs regularly, and appear for doctor visits when recommended by the doctor or when they have any complaints in order to identify the problems early.