VEGFB, as known as VRF, is a member of the VEGF family of growth factors that share structural and functional similarity. By alternative splicing, two isoforms of mature VEGF-B containing 167 or 186 amino acid (aa) residues exist. VEGF-B is expressed in most tissues, especially in heart, skeletal muscle and pancreas. The two VEGF-B isoforms have identical amino-terminal cysteine-knot VEGF homology domains but the carboxyl end of VEGF-B167 differs from that of VEGF-B186 by the presence of a highly basic cysteine-rich heparin binding domain. VEGF-B167 and a proteolytically processed form of VEGF-B186 also bind neuropilin-1, a type I transmembrane receptor for semaphorins/collapsins, ligands involved in neuron guidance.