A two-year international study of more than 17,000 heart patients showed that aspirin and the clot-dissolving drug streptokinase, taken together after the onset of chest pains, reduce deaths among heart attack victims. The Second International Study on Infarct Survival, involving patients in 400 hospitals in 16 countries, is billed as the largest heart attack treatment study ever. It was presented Tuesday at the annual meeting of the American College of Cardiology in Atlanta. The study showed that a chewed aspirin tablet or administration of the drug streptokinase, or SK, improved the survival rate. The rate improved more, however, when the two were taken together.