However, under certain types of stress or injury (e.g., hypoxia, pressure/volume overload), the heart produces pro-fibrotic factors, such as transforming growth factor (TGF)-β1, angiotensin II (Ang-II), and platelet-derived growth factor (PDGF), which can transform CF into myofibroblasts. This evidence concerns the gene TGFB1 and cystic fibrosis.