Pulmonary arterial hypertension (PAH) is a rare and severe disease characterized by elevation of pulmonary artery pressure (PAP) and increased pulmonary vascular resistance (PVR) due to the narrowing of small pulmonary arteries. The European Society of Cardiology (ESC) and the European Respiratory Society (ERS) recommend supervised exercise-based rehabilitation as part of the treatment of PAH patients alongside optimal medical therapy (Level of evidence A, Class of recommendation I). Studies on exercise-based rehabilitation for PAH patients are limited, and most interventions have been conducted at least partially in hospital settings. Unlike more common cardiovascular diseases, there are no detailed international exercise guidelines tailored specifically for PAH patients. This study aims to verify that a group-based outpatient rehabilitation protocol suitable for the Finnish healthcare system improves exercise capacity, quality of life, and physical activity of PAH patients and is safe for appropriately selected patients. Additionally, the study aims to determine whether PAH patients adhere to regular exercise training and whether physical activity increases in the long term. The goal is to assess whether an outpatient rehabilitation protocol, designed for the Finnish healthcare system, can achieve similar results to those observed in previous international studies. The primary outcome measure is the change in the six-minute walking distance (6MWD) compared to the patient's baseline. Long-term 6MWD data are often available for patients. The 6MWD is the most commonly used primary outcome in randomized and controlled PAH drug trials, and improvements in this test have been the basis for drug approvals. An improvement of 33 meters in the 6MWD is considered clinically significant, and the goal is to achieve this change with group-based outpatient rehabilitation. Secondary outcomes include changes in quality of life (SF-36), WHO functional class, NT-proBNP levels, echocardiographic parameters, ESC/ERS risk-stratification score (four-strata model), muscle strength, respiratory measures, balance, daily step count, and insomnia severity.