Study of the Efficacy and Safety of Tezosentan in Patients With Pre-operative Pulmonary Hypertension, Due to Left Heart Disease, Undergoing Open Heart Surgery

Inclusion Criteria: * Patients ≥ 18 years of age * Male or female patients (females of child-bearing potential must have been surgically sterilized or use a reliable method of contraception). * Patients undergoing complex\* cardiac surgery on CPB and having systolic PAP \> 40 mmHg or mean PAP \> 30 mmHg (\*surgery on 2 valves, 1 valve and revascularization, or reoperation of a valve) * Patients undergoing cardiac surgery on CPB and having pre-operative pulmonary hypertension due to left heart disease with systolic PAP \> 60 mmHg * Signed written informed consent Exclusion Criteria: * Systolic blood pressure \< 100 mmHg * Significant chronic lung disease * Emergency surgery * Pregnant/breast-feeding * Investigational drug use within 28 days prior to randomization * Complex adult congenital heart disease. * Severe concomitant illness limiting life expectancy to \< 6 months * Participation in a device study that will affect the outcome of the study * Pre-operative use of balloon pump, inotropes/vasopressors, treatment of pulmonary arterial hypertension * Known hypersensitivity to tezosentan or drugs of the same class, or any of their excipients * Severe liver impairment