Nitroglycerin relaxes the arteries and veins. It pools the blood in the extremities dropping blood pressure. Chest pain relief can be expected in 1-3 minutes. Because it is administered sublingually, it is absorbed directly in the bloodstream. If the chest pain did not improve in 5 minutes, it should be repeated. It can be repeated the third time( after 5 minutes from second dose). If the pain doesn't subside after 3 doses, emergency care is needed.