Thrombosis, the clogging of blood vessels, is a major cause of heart attacks and embolism. Scientists have now engineered the first inhibitors of thrombin, a protease promoting thrombosis, that is three-fold efficient. In a study published in the journal Angewandte Chemie, the authors demonstrate that attacking three sites of the thrombin molecule is more efficient than attacking only two sites, which is the mode of action of many natural agents.