This is thrombosis in the left anterior descending coronary artery opened longitudinally here over the surface of the heart. This is another complication of atherosclerosis. The purpose of thrombolytic therapy (as with streptokinase or with tissue plasminogen activator, or TPA) is to dissolve recently formed thrombi and re-establish circulation before irreversible myocardial damage has been done, or at least to prevent additional myocardial injury.