The 6-minute walk test was conducted according to the American Thoracic Society guidelines in accordance with local standard operating procedures. 6MWD was measured by a 6-minute walk test. This test measures the distance that a participant can walk in a period of 6 minutes. Change from baseline was calculated at Weeks 4, 8, 12 and 16. Change from Baseline was calculated as value at the specified visit minus the Baseline value. Data at Baseline is based on average of two consecutive test results during Screening/Baseline period that differ by <10%. If only one measurement was available, that measurement was used. In any cases where the protocol-defined criteria for Baseline 6MWD was not met, the Baseline value was based on the last two consecutive measurements for a participant.

Intent-to-Treat (ITT) Population: comprised of all randomized participants who received at least 1 dose of study drug. Only those participants with available data at Baseline and the specified timepoint (represented as n=X, X for placebo and ambrisentan respectively) were summarized.

PVR is a measure of cardiopulmonary haemodynamics. Change from Baseline was calculated as value at specified visit minus Baseline value. Baseline is the last value recorded on or prior to start of study treatment.

ITT Population. Only those participants with available data at Baseline and the specified timepoint were analysed.

The WHO FC indicates the severity of PAH and is an adaptation of the New York Heart Association classification. It was assessed by the investigator. There are four grades for WHO FC based on severity of symptoms (Class I = none, Class IV = most severe). This functional classification system links symptoms with activity limitations, and allows clinicians to quickly predict disease progression and prognosis, as well as the need for specific treatment regimens, irrespective of the underlying etiology of PAH. Baseline is the last value recorded on or prior to start of study treatment. Change from Baseline was calculated as the value at specified visit minus the Baseline value. For analyse purposes, the WHO FC Class categories of I-IV were mapped to a numeric scale of 1-4.

Intent-to-Treat (ITT) Population: comprised of all randomized participants who received at least 1 dose of study drug. Only those participants with available data at Baseline and the specified timepoint (represented as n=X, X for placebo and ambrisentan respectively) were summarized.

The BCR10S score was collected immediately following completion of the 6-minute walk test. Baseline data was calculated as the average of the two BCR10S values obtained following the two 6MWD tests used in determining the Baseline 6MWD. If only one measurement was available, that measurement has been used. BCR10S scores ranges from 0 to 10 (0=nothing at all, 10=extremely strong). If participant's perception or feeling was stronger than "10", i.e "extremely strong", "Maximal" - a larger number could be used, e.g. 12 or still higher i.e "Absolute maximum"). Change from Baseline was calculated as the value at specified visit minus the Baseline value.

Intent-to-Treat (ITT) Population: comprised of all randomized participants who received at least 1 dose of study drug. Only those participants with available data at Baseline and the specified timepoint (represented as n=X, X for placebo and ambrisentan respectively) were summarized.

Clinical worsening of CTEPH is defined by the time from randomization to the first occurrence of death, lung transplantation, hospitalization for CTEPH, atrial septostomy, addition of parenteral prostanoids, or study withdrawal due to two or more early escape criteria included: a decrease from Baseline of at least 20 percent in the distance walked during the six-minute walk test; an increase of one or more WHO functional class; worsening right ventricular failure (e.g., as indicated by increased jugular venous pressure; new/worsening hepatomegaly, ascites, or peripheral edema; worsening echocardiographic parameters such as tricuspid annulus plane systolic excursion (TAPSE) and Tissue Doppler Imaging of the tricuspid annulus); rapidly progressing cardiogenic, hepatic, or renal failure; refractory systolic hypotension (systolic blood pressure less than 85 millimeter of mercury [mmHg]).

ITT Population

mPAP and mRAP are measures of cardiopulmonary hemodynamics. Baseline is the last value recorded on or prior to start of study treatment. Change from Baseline was calculated as the value at specified visit minus the Baseline value.

Intent-to-Treat (ITT) Population: comprised of all randomized participants who received at least 1 dose of study drug. Only those participants with available data at Baseline and the specified timepoint (represented as n=X, X for placebo and ambrisentan respectively) were summarized.

Cardiac index is measure of cardiopulmonary hemodynamics. Baseline is the last value recorded on or prior to start of study treatment. Change from Baseline was calculated as the value at specified visit minus the Baseline value.

Intent-to-Treat (ITT) Population: comprised of all randomized participants who received at least 1 dose of study drug. Only those participants with available data at Baseline and the specified timepoint were summarized.

The ratio to baseline [BL] in NT-proBNP was calculated as the ratio of the value at the specified time-point to the BL value and was expressed as a percent change from BL. For each treatment group, the mean change from BL at the specified time-point was determined on the log scale. This mean was then back transformed to give a geometric mean (GM) of the ratio of the value at the specified time-point to BL on the original scale. The GM was expressed as a percentage (100*[GM - 1]). Standard Deviation(SD) is the SD of the mean change from baseline values on the log scale.

Intent-to-Treat (ITT) Population: comprised of all randomized participants who received at least 1 dose of study drug. Only those participants with available data at Baseline and the specified timepoint (represented as n=X, X for placebo and ambrisentan respectively) were summarized.

The SF-36 v2 is a self-administered, health-related quality of life (QoL) metric. It is a 36-item questionnaire designed to measure 8 domains of functional health status and well-being: physical functioning, role-physical, bodily pain, general health perceptions, vitality, social functioning, role-emotional, and mental health as well as 2 summary measures (Physical Health and Mental Health). Each domain is scored from 0 (poorer health) to 100 (better health). Change from Baseline was calculated as the post-Baseline score minus the Baseline score. The SF-36 data were collected, but after the study was terminated, not all endpoints listed in the protocol were analyzed, including the SF-36. This decision was documented in the reporting and analysis plan prior to database lock.

ITT Population

AE is defined as any unfavorable and unintended sign (including an abnormal laboratory finding), symptom, or disease (new or exacerbated) temporally associated with the use of a medicinal product. For marketed medicinal products, this also includes failure to produce expected benefits (i.e., lack of efficacy), abuse or misuse. A SAE is defined as any untoward medical occurrence that, at any dose results in death, is life-threatening, requires hospitalization or prolongation of existing hospitalization, results in disability/incapacity or is a congenital anomaly/birth defect or important medical events that may not be immediately life-threatening or result in death or hospitalization but may jeopardize the participant or may require medical or surgical intervention to prevent one of the other outcomes listed in the above definition.

ITT Population

Haemoglobin levels were assessed at Screening, Baseline, Weeks 4, 8, 12, and 16/Early Withdrawal. Baseline is the last value recorded on or prior to start of study treatment. Change from Baseline was calculated as the post-Baseline value minus the Baseline value.

Intent-to-Treat (ITT) Population: comprised of all randomized participants who received at least 1 dose of study drug. Only those participants with available data at Baseline and the specified timepoint (represented as n=X, X for placebo and ambrisentan respectively) were summarized.

Haematocrit levels were assessed at Screening, Baseline, Weeks 4, 8, 12, and 16/Early Withdrawal. Baseline is the last value recorded on or prior to start of study treatment. Change from Baseline was calculated as the post-Baseline value minus the Baseline value.

Intent-to-Treat (ITT) Population: comprised of all randomized participants who received at least 1 dose of study drug. Only those participants with available data at Baseline and the specified timepoint (represented as n=X, X for placebo and ambrisentan respectively) were summarized.

A significant liver chemistry result is defined as any result which met the stopping criteria defined in the study protocol. Liver events were assessed at Screening, Baseline, Weeks 4, 8, 12, and 16/Early Withdrawal. Number of participants who reported a significant liver chemistry result are presented.

ITT Population

Vital sign measurements including supine systolic and diastolic blood pressure at Weeks 4, 8, 12, and 16/Early Withdrawal weeks. Supine blood pressure measurement was taken in a supine position having rested in this position for at least 10 minutes before each reading. Baseline is the last value recorded on or prior to start of study treatment. Change from Baseline was calculated as the post-Baseline value minus the Baseline value.

Intent-to-Treat (ITT) Population: comprised of all randomized participants who received at least 1 dose of study drug. Only those participants with available data at Baseline and the specified timepoint (represented as n=X, X for placebo and ambrisentan respectively) were summarized.

Vital sign measurements including heart rate at Weeks 4, 8, 12, and 16/Early Withdrawal weeks. Baseline is the last value recorded on or prior to start of study treatment. Change from Baseline was calculated as the post-Baseline value minus the Baseline value.

Intent-to-Treat (ITT) Population: comprised of all randomized participants who received at least 1 dose of study drug. Only those participants with available data at Baseline and the specified timepoint (represented as n=X, X for placebo and ambrisentan respectively) were summarized.

Clinical chemistry parameters including alanine amino transferase (ALT), aspartate amino transferase (AST), creatinine, gamma glutamyl transferase (GGT) and total bilirubin (TB) assessed any time post Baseline. ALT: lower concern value and high concern value was considered as none and >=3xupper limit of normal (ULN) respectively. AST: lower concern value and high concern value was considered as none or >=3xULN respectively. creatinine: lower concern value and high concern value was considered as none and >=176.8 micromoles per liter (umol/L) respectively. GGT: lower concern value and high concern value was considered as none and >=3xULN respectively. For TB: lower concern value was none and high concern value was >=2xULN. Participants with both normal and low values were counted once under their worst case (Low). Participants with both normal and high values were counted once under their worst case (High). Participants with both high and low values are counted under both categories.

ITT Population

Hematology parameters including hemoglobin, international normalized ratio (INR), and platelet count assessed any time post Baseline. Baseline is the last value recorded on or prior to start of study treatment. For hemoglobin: lower concern value and high concern value was considered as <100 gram per liter (G/L) and none respectively. For INR: lower concern value and high concern value was considered as none or >5 prothrombin time respectively. For platelet count: lower concern value and high concern value was considered as <50 giga cells per liter (GI/L) and >500 GI/L respectively. Participants with both normal and low values were counted once under their worst case (Low). Participants with both normal and high values were counted once under their worst case (High). Participants with both high and low values are counted under both categories.

Intent-to-Treat (ITT) Population: comprised of all randomized participants who received at least 1 dose of study drug. Only those participants with available data at Baseline and the specified timepoint (represented as n=X, X for placebo and ambrisentan respectively) were summarized.

For male participants testicular function (total testosterone, sex hormone binding globulin [SHBG-calculated free testosterone), follicle stimulating hormone (FSH), luteinizing hormone (LH), and inhibin B were assessed at Weeks 4 and 16/early withdrawal. The testicular function data were collected, but after the study was terminated, not all endpoints listed in the protocol were analyzed, including Testicular Function. This decision was documented in the reporting and analysis plan prior to database lock.](streamdown:incomplete-link)

ITT Population