Long-term Ambrisentan Extension Study for Pediatric Patients Who Participated in AMB112529

An open label, long term extension to Study AMB112529. All subjects may remain in the extension study for a minimum of six months. Beyond the six month period, subjects may continue in the extension study until one of the following conditions is met: the subject turns 18 years of age (when the subject can receive marketed product) the product is approved and available for use in the subject's age group, development for use in the paediatric population is discontinued. the subject decides he/she no longer wants to participate in the study, the investigator considers it is in the best interest of the subject to discontinue ambrisentan (e.g. for safety reasons). The primary objective is the long-term safety and tolerability of ambrisentan in the paediatric PAH population. Secondary objectives are all cause mortality and change from baseline in Study AMB112529 on efficacy parameters.