Heart attacks and strokes are caused by blood clots called thrombi that block blood flow in the arteries of the heart and of the brain. Body tissues become deprived of needed oxygen and nutrients, eventually dying. Cardiovascular disease is the number one killer of Americans each year — and has been since 1900 with the exception of one year, according to a recent report by the American Heart Association. Harvard Medical School student Ryan Turner has spent the last year doggedly researching plasmin, a naturally occurring enzyme in the body with the primary responsibility of dissolving blood clots. Specifically, plasmin attacks fibrin, a substance that makes up clots. A protein inhibitor called alpha 2-antiplasmin in blood stops the clot-busting effects of plasmin. Unfortunately, the quick action of alpha 2-antiplasmin is sometimes too fast, leaving clots in the body to do their damage. “What I endeavored to do was to take plasmin and allow it to stay around longer in the body, increase its half-life so to speak, make it resistant to its natural inhibitor,” said Turner. To achieve his goal, Turner engineered a new form of plasmin. Turner’s discovery has implications for treatment of strokes and heart attacks.