Retrograde autologous priming (RAP) is a non-drug blood protection method to reduce blood dilution by lowering the amount of crystal liquid priming.1, 2, 3 But there is no unified blood transfusion standard. Therefore, we conducted a prospective randomized trial to determine whether RAP can reduce blood transfusion during and after cardiac surgery in adults. 120 adult patients scheduled for cardiac surgery were included. The patients were randomly assigned to the standard priming group (n = 60) or RAP group (n = 60). During anesthesia, the mean arterial pressure (MAP) was maintained above 70 mmHg before cardiopulmonary bypass (CPB) and above 60 mmHg after CPB. The CPB management included alpha-stat pH management, maintaining a MAP between 50 and 80 mmHg, and keeping the pump flow rate at 2.0–2.4 L/min⁻¹/m⁻². Mediastinal blood suction and left heart suction were performed by two rolling pumps. The RAP technique was conducted as follows: Recirculation bag was connected to the exhaust valve of the arterial filter. After completion of the aortic intubation, the patient’s blood was used to replace the priming solution in the arterial duct to the recirculation bag. Then the arterial duct connecting the patient was clamped. Once the venous conduit was connected to the venous cannula, the flow occlusion clamp was released to allow the venous blood to flow out. Simultaneously, the arterial pump maintained the fluid level of the blood reservoir at a proper flow rate (400–600 mL/min). The crystal priming solution in the blood reservoir was placed back into the recovery bag and maintained at the lowest level; the venous end was opened. The liquid mixture in the blood reservoir was slowly pumped into the arterial filter, membrane oxygenator. Full-flow CPB was then established with the arterial and venous clamps opened and pump flow increased. The RAP took place 3–5 min before the CPB. All patients were successfully discharged. Before CPB, the average priming volume was 1500 mL in the standard priming group, while in the RAP group 610.9 ± 136.2 mL of priming solution was replaced. Of the patients who received a blood transfusion during CPB, the patients in the RAP group received less PRBCs than those in the standard priming group (Table 1). The hematocrit (HCT) value was significantly higher in the RAP group than in the standard priming group at 10 min after aortic occlusion and 10 min after aortic opening. It has been reported that compared with conventional CPB and minimal extracorporeal circulation systems, RAP can reduce hemodilution and the blood transfusion rate during and after operation.⁴ In this experiment, the lowest HCT value during CPB in the study group was significantly higher and only 20% of patients received a blood transfusion. The overall transfusion rate and intraoperative transfusion volume of homologous PRBC units in the RAP group were lower than those in the standard priming group.