Unfractionated heparin (UFH) is the standard anticoagulant for inhibiting the formation of blood clots in patients who undergo cardiopulmonary bypass, which allows cardiac procedures to be carried out in a motionless, bloodless surgical field and is performed annually on more than one million patients worldwide. Although UFH is strongly effective, it carries the risk of post-operative bleeding and is potentially harmful or even deadly in certain patients. An alternative anticoagulant called 11F7t might reduce the risk of common clinical complications of UFH, but it is less potent. New findings suggest that combining 11F7t with clinically approved anticoagulants called factor Xa inhibitors may prevent the formation of blood clots during cardiopulmonary bypass as effectively as UFH and more effectively than either agent alone, while avoiding the side effects of UFH. However, preclinical studies in mammals are needed to further test this possibility. The study, which was published in Nature Biotechnology, was partly funded by NHLBI.