Conflict of interest: M.M. Hoeper reports receiving personal fees from Actelion, Bayer, GSK, Pfizer, Gilead and Merck, during the conduct of the study. Conflict of interest: D. Pittrow reports receiving personal fees from Actelion, Aspen, Bayer, Boehringer Ingelheim, Daiichi Sankyo, Novartis, Pfizer and AstraZeneca, outside the submitted work. Conflict of interest: C. Opitz reports receving personal fees from Actelion, Bayer, GSK, Pfizer and Novartis, during the conduct of the study. Conflict of interest: J.S.R. Gibbs reports receiving personal fees from Actelion, Bayer, GSK, Pfizer, MSD, Bellerophon and Arena, during the conduct of the study. Conflict of interest: S. Rosenkranz reports receving grants and personal fees from Actelion, Bayer, Pfizer, Novartis and United Therapeutics, and personal fees from GSK, Gilead and MSD, during the conduct of the study. Conflict of interest: E. Grünig reports receiving personal fees from Actelion, Bayer, GSK, Pfizer, United Therapeutics and MSD, outside the submitted work. Conflict of interest: K.M. Olsson reports receiving personal fees from Actelion, Bayer, GSK, Pfizer and United Therapeutics, during the conduct of the study. Conflict of interest: D. Huscher reports receiving personal fees from Actelion outside the submitted work.