Usually, small specialized structures inside each human cell called mitochondria are in charge of generating energy within lung arteries for normal function. During situations of disease or stress, lung arteries undergo a change in teh function of mitochondria, resulting in the development of PH. In studies on mice, investigators have learned that alterations in the production of specific metal complexes called iron-sulfur clusters are responsible for these changes. This makes it more likely that mice will develop PH.