During cardiac surgery on cardiopulmonary bypass (CPB), complement activation -- a rapid and intense inflammatory response -- can occur. Complement activation can be triggered when blood flow is restored to oxygen-deprived tissue and through exposure to the heart-lung machine. This inflammatory response can damage heart and lung function and can contribute significantly to post-operative complications that impair patient recovery. The result can be prolonged hospital stays and increased medical expenses. Complement activation is also central to acute inflammatory reactions -- notably vascular diseases like stroke and heart attack, where tissue damage is highly localized.