This study focuses on individuals who have pulmonary arterial hypertension (PAH). PAH is caused by a narrowing of the blood vessels that connect the lungs to the heart and leads to an increase in the pressure inside these blood vessels. The purpose of the study is to evaluate the effects of an investigational drug called AV-101 for the treatment of PAH. AV-101 is a dry powder that is inhaled into the lungs via the mouth; it is involved in blocking enzymes that may activate proteins that cause the pulmonary artery to thicken. Participants will be randomly assigned to receive either AV-101 or placebo/inactive substance (1 in 4 chance of receiving placebo).