['Formation of microthrombi after circulatory arrest is a concern for the development of reperfusion injury in lung recipients from donation after circulatory death (DCD) donors. In this isolated lung reperfusion study, we compared the effect of postmortem heparinization with preharvest retrograde pulmonary flush or both.', 'Domestic pigs (n\xa0=\xa06/group) were sacrificed by ventricular fibrillation and left at room temperature for 1\xa0h. This was followed by 2.5\xa0h of topical cooling. In control group [C], no heparin and no pulmonary flush were administered. In group [R], lungs were flushed with Perfadex in a retrograde way before explantation. In group [H], heparin (300\xa0IU/kg) was administered 10\xa0min after cardiac arrest followed by closed chest massage for 2\xa0min. In the combined group, animals were heparinized and the lungs were explanted after retrograde flush [HR]. The left lung was assessed for 60\xa0min in an ex\xa0vivo reperfusion model.', 'Pulmonary vascular resistance at 50 and 55\xa0min was significantly lower in [R] and [HR] groups compared with [C] and [H] groups (P\xa0<\xa00.01 and P\xa0<\xa00.001) and at 60\xa0min in [R], [H], and [HR] groups compared with [C] group (P\xa0<\xa00.001). Oxygenation, compliance, and plateau airway pressure were more stable in [R] and [HR] groups. Plateau airway pressure was significantly lower in [R] group compared with the [H] group at 60\xa0min (P\xa0<\xa00.05). No significant differences in wet-dry weight ratio were observed between the groups.'] Is retrograde flush more protective than heparin in the uncontrolled donation after circulatory death lung donor?