Abstract Background Pulmonary arterial hypertension (PAH) is a rare, complex and chronic disease, characterised by a mean pulmonary arterial pressure at rest above 20 mmHg, determined through right heart catheterisation. As the disease progresses, symptoms (e.g., chest pain, syncope, respiratory distress) occur, which negatively impact quality of life. Moreover, symptoms of PAH can impair activities of daily living and social functions, leading to social isolation and loneliness. So far the experience of social isolation and loneliness in PAH patients. Purpose To explore the lived experience of social isolation and loneliness in patients with PAH. Methods A multicentre descriptive phenomenological study was conducted with semi-structured interviews driven by the Middle Range Theory of Social Isolation. This study followed the COREQ guidelines, and data analysis was conducted using the Elo and Kyngäs method. Results Seventeen patients (mean age 55,3 years; range 21-83 years; n=3 male) recruited from specialized clinics or patient associations across different Italian regions, participated in the interviews. The results show that patients with a marked symptomatology experience daily moments of loneliness and social isolation that inevitably impact the quality of life. While, patients with a mild symptomatology or with drug support can lead a life similar to that before diagnosis. Three main categories emerged. First, within the main category of loneliness emerged generic categories including emotions associated with loneliness (anger, depression, frustration, guilt, fear)as well as the influence of loneliness on the disease and the various strategies to limit it. Second, for the main category of social isolation were also identified other generic categories including networks of support of the person with PAH (family, social and work), emotions related to social isolation (dismissal and pretend to be well) and the influence of social isolation on the path of illness. Finally, generic categories related to well-being, autonomy, health, self-care activity or health promotion performed by the patient emerged for the main quality of life category. Conclusion The findings of this study contribute to a more in depth understanding of the factors influencing the quality of life of patients with PAH and enlighten the design of interventions aimed at improving their condition. Integration of these results with quantitative data regarding the extent of the influence of loneliness and social isolation is warranted.