Number of subjects with categorized change in 6-minute walking distance. Distance that a subject could walk in 6-minutes at a comfortable pace with as many breaks as needed. Performed as close to trough levels of sildenafil as possible (just before dosing; at least 4 hours after the previous dose of study drug). Scores for categorized changes for missing visits were imputed as the worse score of its non-missing neighbors. If a visit was missing and there was no subsequent score, the score was coded to missing.

Yearly survival status: number of subjects who survived, discontinued, and died. Analysis includes post-treatment visit data from subjects who discontinued study treatment. Time to death was taken relative to the first dose of study treatment in A1481141, and was censored on the last day the subject was known to be alive in A1481141 or A1481153.

Pulmonary hypertension (PH) criteria: Class I: PH without limitation of physical activity (PA) (no undue dyspnea, fatigue, chest pain, near syncope); Class II: PH with slight limitation in PA, comfortable at rest, ordinary PA causes undue dyspnea, fatigue, chest pain, near syncope; Class III: PH with marked limitation in PA, comfortable at rest, less than ordinary activity causes undue dyspnea, fatigue, chest pain or syncope; Class IV: PH with inability to carry out PA without symptoms, signs of right heart failure, dyspnea or fatigue may be present at rest, discomfort increased by any PA.

Subject-rated measure of health status comprised of 36 items: 8 subscale scores (physical functioning, role limitations due to physical health problems, bodily pain, general health, vitality, social functioning, role limitations due to emotional problems, and mental health), 2 summary scores (physical component and mental component), and a self-evaluated change in health status. Subscale and summary scores range: 0-100. Higher subscale and summary scores = better health status. Change from baseline = score at observation minus score at baseline.

EQ-5D: subject rated questionnaire to assess health-related quality of life in terms of a single utility score. Health State Profile component assesses level of current health for 5 domains: mobility, self-care, usual activities, pain and discomfort, and anxiety and depression; 1 indicates better health state (no problems); 3 indicates worst health state (confined to bed). Scoring formula developed by EuroQol Group assigns a utility value for each domain in the profile. Score is transformed and results in a total score range -0.594 to 1.000; higher score indicates a better health state.

EQ-5D: subject rated questionnaire to assess health-related quality of life in terms of a single index value. The VAS component rates current health state on a scale from 0 (worst imaginable health state) to 100 (best imaginable health state); higher scores indicate a better health state.

Subject-rated measure of health status (36 items): 8 subscale scores (physical functioning, role limitations due to physical health problems, bodily pain, general health, vitality, social functioning, role limitations due to emotional problems, mental health), 2 summary scores (physical component, mental component), and a self-evaluated change in health status. Change from Baseline in SF-36 Health Transition score at each visit. I=much better than 1 year ago; II=somewhat better than 1 year ago; III=about the same as 1 year ago; IV=somewhat worse than 1 year ago; V=much worse than 1 year ago

BORG Dyspnea score: change from core study Baseline. Subject rating of maximum degree of dyspnea experienced at any time during the 6-Minute Walk Test. Range: 0 (no breathlessness at all) to 10 (maximum breathlessness).