Abstract Background: Patients with Heart Failure with preserved Ejection Fraction (HFpEF) and Pulmonary Hypertension (PH) have increased right atrial (RA) pressures. Whether the higher RA pressures are related to increased afterload or overall stiffening of the heart is unknown. The aim of this study is to gain further insight into the right atrium in HFpEF-PH. Methods: This is a retrospective analysis of patients with HFpEF (no PH), HFpEF-PH and Pulmonary Arterial Hypertension (PAH) that underwent right heart catheterization and cardiac magnetic resonance (CMR) imaging. CMR was used to determine RA function by quantifying volume and strain on the 4-chamber view. Total, passive and active RA emptying fraction (RAEF) were calculated. RA stiffness was calculated by determining the slope of maximum and minimum pressure during v-wave and minimal and maximal RA volumes. Groups were compared with ANOVA and post-hoc comparison with Bonferroni correction. Results: 176 patients were included: 13 HFpEF, 33 HFpEF-PH and 130 PAH patients. Although afterload was lower in PAH and higher in HFpEF patients, as shown by mean pulmonary arterial pressure (mPAP) (41± 2 mmHg in HFpEF-PH vs 53± 21 mmHg in PAH vs 19± 1 mmHg in HFpEF, p<0.001) and pulmonary vascular resistance (PVR) (2.3± 0.3 wu/m2 in HFpEF-PH vs 5.7± 0.2 wu/m2 in PAH vs 0.4± 0.06 wu/m2 in HFpEF, p<0.001), mean RA pressure was significantly higher in HFpEF-PH patients compared to both groups (Figure 1A). HFpEF-PH patients had significantly increased RA stiffness compared to HFpEF and PAH patients (Figure 1B). Total RAEF was reduced in HFpEF-PH compared to PAH and HFpEF patients: passive RAEF was similar, but active RAEF was slightly reduced in HFpEF-PH (Figure 1C). This was in line with measurements of RA longitudinal strain (Figure 1D). Conclusions: Despite lower afterload, HFpEF-PH patients have worse RA function and increased RA stiffness compared to PAH. Higher RA pressures in HFpEF-PH may reflect additional stiffening of the heart.