Background: Sleep disordered breathing (SDB) is well known to be associated with increased mortality in patients with left-heart failure, however the clinical significance of SDB in patients with pulmonary hypertension (PH) is not established. We sought to investigate the association of SDB with hemodynamic parameters and serum troponin T concentrations in patients with PH. Methods and Results: Overnight polygraphy was performed in 107 clinically stable patients with PH (pulmonary arterial hypertension n=52 [idiopathic n=23, collagen disease n=11, congenital heart disease n=6, others n=12]and chronic thromboembolic PH n=55), and evaluated apnea-hypopnea index (AHI; 7.6±9.3, obstructive apnea 1.8, central apnea 0.4, and hypopnea 5.3 events/h). Based on AHI, these patients were divided into two groups: non SDB (AHI<15/h, n = 90) and SDB groups (AHI≧15/h, n = 17). The presence of SDB was associated with older age (p<0.05), but not associated with gender, BMI, smoking, and the presence of hypertension, dyslipidemia, and diabetes mellitus. Hemodynamic studies showed that SDB patients had higher mean pulmonary artery pressure (mPA; 38±13 vs. 31±12 mmHg, p<0.05), higher pulmonary vascular resistance (PVR; 9.4±7.5 vs. 5.2±3.6 Wood, p<0.05) and lower cardiac output (3.4±0.9 vs. 4.8±1.9 L/min, p<0.05), but PCWP did not differ between two groups. In laboratory study, plasma BNP and serum CRP levels were not associated with SDB. However, high-sensitivity troponin T (hsTnT) level was significantly higher in patients with SDB than those without (0.017±0.014 vs. 0.008±0.006 ng/mL; p<0.05). HsTnT level positively correlated with plasma BNP level, mPA, PVR, and WHO functional class, and negatively correlated with cardiac output and 6 minute-walking distance (all p<0.05). Furthermore, after adjustment for age, lower eGFR, hypertension, smoking, and plasma BNP level in multiple regression analysis, the presence of SDB was the independent factor to determine plasma level of log hsTnT (β = 0.19, p<0.05). Conclusions: SDB is associated with subclinical myocardial damage and disease severity in patients with PH, suggesting the role of SDB-related myocardial injury in the vicious circle leading to hemodynamics destabilization and adverse prognosis.