
    number of candidates for this study is expected to be too small.
  
['hypertension, pulmonary', 'diseases of mitral valve']
['sildenafil', 'placebo']

        Inclusion Criteria:

          -  New York Heart Association Functional class (NYHA Fc) ≥ 2 dyspnea which was sustained
             till one year after the previous mitral valve surgery (repair or replacement)

          -  TR Vmax ≥ 3.5m/s by echocardiography

          -  Normal left ventricle ejection fraction (EF ≥ 50%)

          -  Pulmonary vascular resistance ≥ 3 Wood Unit or diastolic pressure gradient ≥ 7mmHg by
             cardiac catheterization

        Exclusion Criteria:

          -  Other valve disease more than moderate degree (ex. aortic stenosis, aortic
             regurgitation)

          -  Liver cirrhosis

          -  Chronic renal failure with serum creatinine ≥ 1.7mg/dL

          -  Lung disease (ex. chronic obstructive pulmonary disease, Asthma)

          -  Thyroid dysfunction

          -  Other causes which can lead to pulmonary hypertension
      