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Coronary artery blockage of that extent is suggestive that it will cause breathlessness even at rest soon if you left it progress. Little exertion also could precipitate heart attack
. You have no other go than angioplasty
or CABG. You need to modify your lifestyle. STOP SMOKING
. Avoid junk food, fatty food. Eat plenty of fresh fruits and vegetables. Drink enough water. Avoid stress in daily life by meditation
, Pranayam and Yoga.