A Study to Evaluate Efficacy and Safety of Oral BAY63-2521 in Patients With CTEPH.

Pulmonary Vascular Resistance (PVR) - Change From Baseline to Week 16

The pulmonary vascular resistance (PVR) is a calculated hemodynamic parameter. PVR is derived from the directly measured parameters mean pulmonary arterial pressure (PAPmean) and pulmonary capillary wedge pressure (PCWP), divided by the cardiac output (CO). PVR and PAPmean are acquired during a right heart catheterization. CO is a calculated hemodynamic parameter, too. Formula: PVR = 80\*(PAPmean - PCWP)/CO

Time frame: Baseline and week 16

N-terminal Prohormone of Brain Natriuretic Peptide (NT-proBNP) - Change From Baseline to Week 16

N-terminal pro-brain natriuretic peptide (NT-proBNP) levels in the blood are used for screening, diagnosis of acute congestive heart failure (CHF) and may be useful to establish prognosis in heart failure.

Time frame: Baseline and week 16

World Health Organization (WHO) Functional Class - Change From Baseline to Week 16

The WHO functional assessment of pulmonary arterial hypertension ranged from functional class I (Patients with PH but without resulting limitation of physical activity) to class IV (Patients with PH with inability to carry out any physical activity without symptoms. These patients manifest signs of right-heart failure.). Changes to a lower WHO functional class resemble improvement; changes to a higher functional class resemble deterioration of PAH.

Time frame: Baseline and week 16

Percentage of Participants With Clinical Worsening

The combined endpoint "time to clinical worsening", made up of the following components, defined by the first occurrence: all-cause mortality; heart/lung transplantation; rescue endarterectomy; first hospitalization due to pulmonary hypertension; start of a new pulmonary hypertension treatment; persistent worsening of 6MWD or WHO functional class due to deterioration of PH.