With more than 25 centuries of efforts to resolve its mysteries, the pulmonary circulation continues to inspire and humble researchers, frustrate clinicians, and scare patients with pulmonary arterial hypertension (PAH). Its mysteries lie in lost manuscripts written in the 12th-century Syria; within the pages of one of the rarest books in history written in 1531 by an author burned alive with his books, condemned by the Inquisition; within a publication from a young urologist self-experimenting 30 years before he received the Nobel prize…What kind of disease is this one that in the age of planning missions to Mars, no medical therapy can save its victims? It is certainly a disease that deserves our respect. The objective of this compendium is to present the state of the art in PAH, but mostly emphasize its future, discussing several evolving theories on its pathogenesis. Its objective is also to comprehensively summarize our current clinical approach to the disease, with patients in mind. In addition to researchers, clinicians, health professionals, students, and residents, its target audience includes patients: the patients who suffer, desperate for answers, and the patients who, one way or another, not only participate in but also fund our research through their taxes and donations. In the age of instant and easy information dissemination, many patients are already quite informed when they visit a specialist. How do we describe the cutting-edge developments in this complex disease to the informed patient? It is not easy, but most would agree that only the expert who really understands his/her subject is able to describe it in lay terms and pass its main messages. Humbled by the complexity of PAH and its challenges, we need to focus on what drives all of us fighting this disease. In addition to our patients, it is scientific curiosity: PAH …