Resuscitative endovascular balloon occlusion of the aorta (REBOA) is a viable resuscitation approach for a subdiaphragmatic injury that can regulate arterial blood flow. On the other hand, the evaluation of venous or portal venous blood flow during REBOA remains insufficient because invasive cannulation or exposure of the vessel may affect the blood flow, and Doppler echography is highly operator-dependent. However, phase contrast magnetic resonance imaging (PC-MRI) has enabled accurate evaluation and non-invasive measurement. This study aimed to investigate the change of venous and portal venous blood flow during REBOA in a porcine model.Seven pigs were anesthetized, and a REBOA catheter was placed. The blood flows of the inferior vena cava (IVC), hepatic vein (HV), portal vein (PV), and superior vena cava (SVC) were measured using PC-MRI, in both the balloon deflated (No-REBOA) and fully balloon inflated (REBOA) states. Mean arterial pressure (MAP), central venous pressure (CVP), cardiac index (CI) and systemic vascular resistance index (SVRI) were measured.The blood flows of the suprahepatic, infrahepatic, and distal IVC, HV, and PV in the No-REBOA state were 1.40±0.36, 0.94±0.16, 0.50±0.19, 0.060±0.018, and 0.32±0.091 L/min, respectively. The blood flow of each section in the REBOA condition was significantly decreased, at 0.41±0.078 (33% of baseline), 0.15±0.13 (15%), 0.043±0.034 (9%), 0.029±0.017 (37%), and 0.070±0.034 L/min (21%), respectively. The blood flow of the SVC increased significantly in the REBOA condition (1.4±0.63 vs. 0.53±0.14 L/min (257%)). MAP, CVP, CI and SVRI were significantly increased after REBOA inflation.REBOA decreased blood flows of the IVC, HV, and PV and increased blood flow of the SVC. This result could be explained by the collateral flow from the lower body to the SVC. A better understanding of the effect of REBOA on the venous and portal venous systems may help control liver injury.No level of evidence (animal study).