BACKGROUND: Hemodynamic management after out-of-hospital cardiac arrest (OHCA) is critical, yet the impact of vasopressor-driven mean arterial pressure (MAP) targets on pulmonary circulation and right ventricular (RV) function remains unclear. METHODS: In this substudy of the randomized, double-blinded BOX trial, comatose OHCA survivors were allocated to low (63 mmHg) or high (77 mmHg) MAP targets. Pulmonary artery catheters (PAC) were used for serial hemodynamic assessment for 48 h after Intensive Care Unit admission. The primary endpoint was calculated pulmonary vascular resistance (PVR), secondary endpoints included pulmonary capillary wedge pressure (PCWP), pulmonary artery pulsatility index (PAPi), and RV cardiac power output (RV-CPO)-a measurement of RV pumping function. RESULTS: Among 730 included patients (median time randomization to PAC insertion 1.3 h), mPAP was consistently higher in the high-MAP group (mean difference 1.11-1.71 mmHg, 95% CI range 0.12-2.59). Calculated PVR was transiently lower in the high-MAP group during the first 24 h (mean difference -0.16 to -0.30, 95% CI range -0.31 to 0.11), before converging between groups. RV-CPO was lower in the low-MAP group throughout the observation period (mean difference 0.01-0.04 W [95% range 0.00-0.07], with the largest difference at 48 h. PCWP decreased in both groups but was significantly lower in the low-MAP group during the first 12 h (mean difference 1.06-1.40 mmHg, 95% CI range 0.25-2.38). CONCLUSIONS: In comatose OHCA survivors, targeting a higher MAP increased pulmonary artery pressures, PCWP, RV-CPO, heart rate, and cardiac output. The proportionally greater increase in cardiac output over pulmonary artery pressures resulted in a decreased calculated PVR. TRIAL REGISTRATION: ClinicalTrials.gov identifier: NCT03141099. EDITORIAL COMMENT: In this secondary analysis of a subgroup in the BOX out of hospital cardiac arrest treatment trial for oxygen level targets, blood pressure treatment target levels, higher or lower were analyzed, including central circulatory outcomes, using a pulmonary artery catheter. The higher blood pressure target group had accompanying higher pulmonary artery pressures and cardiac output, with initially a small reduction in calculated pulmonary vascular resistance.