The investigators hypothesized that udenafil, a newly developed phosphodiesterase type 5 inhibitor, would improve symptom, exercise capacity and hemodynamic status in patients with mild pulmonary hypertension.

Pulmonary arterial hypertension is a devastating progressive disease increasingly debilitating symptoms. In the past few years, treatment of pulmonary hypertension has undergone an extraordinary evolution. A selective PDE-5 inhibitor, Sildenafil, has been shown to be as an effective pulmonary vasodilator as inhaled NO in patients with primary pulmonary hypertension and has recently been shown to improve exercise capacity, resting hemodynamics, and WHO functional class in patients with pulmonary hypertension. However, to date, the effect of Sildenafil have been mainly studied in patients with advanced disease.

Udenafil (Zydena), a newly developed PDE-5 inhibitor, has been proved to have similar efficacy and safety profile, compared with other PDE-5 inhibitors. However, to date, the effect of Udenafil in mild pulmonary HT has never been evaluated. Therefore, we hypothesized that Udenafil, a newly developed phosphodiesterase type 5 inhibitor, would improve symptom, exercise capacity and hemodynamic status in patients with mild pulmonary hypertension.

In this 12-week, randomized, double-blind, placebo-controlled trial, patients with mild pulmonary hypertension will be enrolled according to the eligibility criteria. After randomization, study participants will be assigned to receive either 50mg of Udenafil or placebo two times a day for 4 weeks, and then the dosage will be doubled to 100mg two times a day for next 8 weeks. Participants will attend study visits at baseline and weeks 4 and 12. Physical examination, medical history review, blood sample collection and electrocardiogram will be conducted on each study visits. At baseline and week 12, participants will undergo cardiopulmonary exercise test and exercise echocardiography. At every study visits, researchers will collect health information.

Inclusion Criteria:

- Mild pulmonary hypertension defined as estimated pulmonary arterial systolic pressure of 30-50 mmHg (TR jet velocity of 2.5-3.4 m/sec) with current New York Heart association (NYHA) class II-IV symptoms, left ventricular ejection fraction (LVEF) greater than or equal to 50% at the time of study entry

Exclusion Criteria:

• Hospitalization for decompensated heart failure or acute treatment with intravenous loop diuretics or hemofiltration in the 12 months before study entry
• E/E' ratio greater than or equal to 15 measured by echocardiography
• E/E' ratio greater than or equal to 8, and left atrial volume index (LAVI) greater than or equal to 40 ml/m2 measured by echocardiography
• E/E' ratio greater than or equal to 8 measured by echocardiography, and plasma BNP concentration greater or equal to 200 pg/ml
• Significant obstructive or restrictive lung disease
• Valve disease (greater than mild stenosis or regurgitation)
• Hypertrophic cardiomyopathy
• Infiltrative or inflammatory myocardial disease
• Pericardial disease
• Primary pulmonary arteriopathy
• Has neuromuscular, orthopedic, or other non-cardiac condition that prevents individual from exercise testing
• Has experienced myocardial infarction or unstable angina, or has undergone percutaneous coronary intervention (PCI) or coronary artery bypass grafting (CABG) within 60 days before study entry
• Non-cardiac illness with estimated life expectancy less than 1 year at the time of study entry, based on the judgment of the physician
• Current use of nitrate therapy
• Current use of other phosphodiesterase 5 inhibitors (ie. sildenafil, vardenafil, tadalafil) for treatment of impotence or pulmonary artery hypertension
• Current use of cytochrome P450 3A4 inhibitors (ie. ketoconazole, itraconazole, erythromycin, saquinavir, cimetidine, protease inhibitors for HIV)
• Severe hypotension (systolic blood pressure [SBP] less than 90mmHg or diastolic blood pressure [DBP] less than 50mmHg) or uncontrolled hypertension (SBP greater than 180mmHg or DBP greater than 100mmHg)
• Known severe renal dysfunction (estimated glomerular filtration rate [GFR] less than 30ml/min/1.73m2 by modified modification of diet in renal disease [MDRD] equation)
• Known severe liver disease (alanine transaminase [ALT] or aspartate aminotransferase [AST] level greater than three times the upper normal limit, alkaline phosphatase [ALP] or total bilirubin greater than two times the upper normal limit)
• History of leukemia, multiple myeloma or penile deformities that increase the risk for priapism (eg. Peyronie's disease)
• History of proliferative diabetic retinopathy, retinitis pigmentosa, nonischemic optic neuropathy, or unexplained visual disturbance
• Female patients currently pregnant or women of childbearing age who were not using contraception