BACKGROUND: This study retrospectively examined the association between elevated trans-pulmonary gradient (TPG), which reflects pre-capillary contribution to pulmonary hypertension (PH), and postoperative pulmonary hemodynamics and outcomes following restrictive mitral annuloplasty (RMA) in patients with pre-existing PH. METHODS: Pre- and postoperative (1 month) cardiac catheterization was performed in 64 patients with severely impaired left ventricular function (i.e., ejection fraction ≤40%) and pre-existing PH (mean pulmonary artery pressure (PAP) ≥25 mmHg) who underwent RMA. Patients were segregated into two groups: low TPG (≤12 mmHg) and elevated TPG (>12 mmHg). The mean follow-up period was 54±27 months. The primary outcome seen was a change in pulmonary hemodynamics after RMA; secondary outcomes were composite adverse events, including all-cause mortality and readmission for heart failure. RESULTS: Compared to the low TPG group, patients in the elevated TPG group were more likely to show a postoperative mean PAP of ≥25 mmHg (84% vs. 38%), TPG of >12 mmHg (79% vs. 11%), and pulmonary vascular resistance of ≥240 dynes/sec/cm-5 (84% vs. 6.7%) (all P<0.001), although both groups showed comparable degrees of mitral regurgitation improvement. Serial echocardiography demonstrated that Doppler-derived systolic PAP, which once decreased in both groups, remained stable in the low group while steadily increasing in the elevated group (group effect P<0.001). Patients with elevated TPG had lower freedom from composite adverse events (5-year, 20% vs. 70%, P=0.003). After adjusting for baseline covariates, the elevated TPG was independently associated with increased risk of adverse events (adjusted hazard ratio 2.9, 95% CI: 1.2-6.9, P=0.017). CONCLUSIONS: Elevated TPG negatively affects postoperative pulmonary hemodynamics and late outcomes in patients with advanced cardiomyopathy and pre-existing PH who have undergone RMA. These findings suggest that the assessment of TPG should be included in post-RMA risk stratification.