Abstract Body (Do not enter title and authors here): Background: There are limited data on the sex differences in the nature history and prognostic factors of asymptomatic pulmonary regurgitation (PR) patients.

Objectives: This study aims to investigate the sex-specific differences in the nature history and clinical prognosis of PR.

Methods: Asymptomatic PR patients undergoing cardiac magnetic resonance at our hospital between 2013 to 2023 were consecutively screened and followed until 2024; baseline characteristics and multimodality imaging variables at the first CMR examination time were assessed. The primary objective was the composite of cardiovascular death, cardiac hospitalization, and pulmonary valve replacement (PVR) events.

Results: Overall, 173 males and 141 females were included. At baseline, females had lower QRS duration, right ventricular (RV) end-diastolic volume index (EDVi), and RV end-systolic volume index (ESVi) than males (All P < 0.05). The risk of the primary objective was higher in females (unadjusted HR: 1.697; 95% CI: 1.157, 2.489), it was even more pronounced after multivariable adjustment. This sexual disparity persisted in adult patients, irrespective of the primary diagnosis. Secondly, QRS > 160ms, RVESVi ≥ 80ml/m², and RVEDVi ≥ 150ml/m² were not sex-specific, whereas RV eject fraction < 47% had predictive value only in females. Additionally, all risks related to these factors were higher in females.

Conclusion: Females have a paradoxical increase in PVR events despite milder RV remodeling at baseline and they maintained a higher risk compared with males across longer QRS, larger RVEDVi and RVESVi, and lower RVEF; these findings suggested that this sexual disparity cannot be ignored when discussing thresholds.