The study by Suntharalingam et al9 randomized 9 patients to receive sildenafil, 40 mg three times daily for 12 weeks, and 10 to receive placebo. The results showed no statistically significant difference in the major outcome variable, the 6-min walk distance, although there was a trend toward an increase in the sildenafil-treated group (17.5 m over the placebo group). As a single-center pilot study, however, it was severely underpowered. Statistically significant improvements were observed in pulmonary vascular resistance and in the quality-of-life instrument used (the Cambridge Pulmonary Hypertension Outcomes Research Score [CAMPHOR]). In addition, among 17 patients in the open-label year-long extension portion of the trial, statistically significant improvements over baseline were noted in the 6-min walk distance (49 m), pulmonary hemodynamics, N-terminal brain natriuretic peptide levels, and CAMPHOR scores. In combination with the previous findings, these lend further support to the idea that patients with inoperable CTEPH respond to pulmonary hypertension drugs like patients with idiopathic PAH.