This study aims to understand how blood cell (including peripheral blood mononuclear cells ((PBMCs) or platelets) function and oxidative stress can help physicians detect and predict the course of pre-capillary pulmonary hypertension. We hypothesize that changes in the mitochondrial function of blood cells and oxidative stress may be early markers of disease progression and severity. The study will also explore how these blood markers relate to routine clinical and heart function measurements, such as echocardiography, right heart catheterization, 6-minute walk tests, and functional status, to see if they can help monitor patients over time and guide personalized care. This is a non-interventional study. Blood samples will be collected during routine visits planned for diagnosis and follow-up. The study will include 120 patients diagnosed with pre-capillary pulmonary hypertension, who will be followed for 3 years. Blood samples will be taken up to three times per year to measure mainly oxidative stress and mitochondrial function in blood cells. These measurements will be compared with clinical tests to see if they can help predict the course of the disease.