Causes of PAH https://www.nivabupa.com/disease-articles/understanding-pulmonary-hypertension-symptoms-causes-and-treatment.html The causes of pah (pulmonary arterial hypertension) include genetic factors, autoimmune diseases like lupus or scleroderma, and conditions such as left heart disease, chronic lung diseases, and blood clots in the lungs. Environmental triggers, including drug use, toxins, and HIV, can also contribute. In some cases, PAH occurs without a known cause, termed idiopathic PAH.