Thrombin generation (TG) is reduced after cardiac surgery using cardiopulmonary bypass (CPB), contributing to coagulopathy and bleeding. Plasma transfusion or four-factor prothrombin complex concentrate (PCC) are commonly used to treat coagulopathic bleeding after CPB without knowledge of how each may restore TG. To determine the effect of PCC infusion on restoration of thrombin generation compared with plasma transfusion, we performed a laboratory-based secondary analysis of a randomized, controlled trial of adult patients undergoing cardiac surgery to assess efficacy and safety of 4 F-PCC versus plasma for treatment of perioperative coagulopathic bleeding after CPB. Participants were randomized to receive either PCC (15 IU/kg) or plasma (10–15 ml/kg) after separation from CPB. Participant blood samples were obtained at pre-specified serial timepoints, with laboratory assays for TG and factor levels subsequently performed. The primary outcome was change in thrombin generation (TG) parameters after each randomized treatment through postoperative day 5. Secondary outcomes included serially derived clotting factor levels. Of 100 randomized participants, 99 were included in this laboratory analysis (PCC group, N = 51; plasma group, N = 48). After treatment, participants in the PCC group compared with those in the plasma group showed higher endogenous thrombin potential (ETP, Median, Interquartile range, IQR: 688 [371–1069] vs. 1088 [550–1691] nM minutes, P = 0.01), a greater increase din ETP (P = 0.002) and peak TG (P = 0.01) in the timepoints between heparin reversal and after treatment administration. Both groups demonstrated similar values in all TG assays by postoperative day 1 (P > 0.05). The PCC group also demonstrated higher levels of proteins C, S, and Factors II, VII, IX and X, early after treatment (P < 0.001 for all comparisons). Antithrombin levels were initially higher in the plasma group after treatment (Median, IQR: 66% [61-71%] vs. 56% [51-65%], P = 0.002) but differences did not persist beyond postoperative day 3. In this laboratory analysis from a recent randomized trial in adult cardiac surgery, PCC administration restored thrombin generation more rapidly than plasma in the early postoperative period without laboratory evidence of hypercoagulability. ClinicalTrials.gov identifier: NCT02557672 [1].