Lack of TFPI increases the susceptibility to thrombosis of Par4^−/− mice in a TF-induced pulmonary embolism model. The time to respiratory arrest after injection of TF was measured. Shown is the percentage of survivors over time. The fraction of surviving Par4^−/− mice is greater than surviving Tfpi^−/−:Par4^−/− mice (P = .0363), and the fraction of both Par4^−/− and Tfpi^−/−:Par4^−/− surviving mice is greater than wild-type mice (P < .0001 and P = .0319, respectively).