One group of animals practiced HIIT for eight weeks, while another group did no exercise. The HIIT group performed seven intervals for seven minutes at 80 to 100 percent of maximum effort, with three minutes at rest between intervals. HIIT increased nitric oxide (NO) levels by 150%. (NO) is a vital chemical produced in the inner lining of the blood vessels that control blood flow. The animals were subjected to decrease heart blood flow to simulate a heart attack. The trained animals suffered substantially less heart damage. Intense interval training protects the heart against reduced blood flow by increasing nitric oxide levels in the coronary arteries.