Respiratory Syncytial Virus (RSV) is a major paediatric viral pathogen of the lower respiratory tract, causing diseases worldwide such as pneumonia and bronchiolitis. RSV uses a virion surface protein, F, to enter host cells by mediating virion-cell and cell-cell fusion, which results in the formation of multinucleate syncytia. The F protein exists in a metastable, pre-fusion fold, that transitions into the energy-favourable, post-fusion structure following receptor engagement. This post-fusion form is stabilized by the formation of a six-helix bundle made of heptad repeats A and B. An additional heptad repeat, heptad repeat C (HRC), was investigated in this project since it is predicted to undergo significant re-arrangement between both protein structures and also lies in close proximity to HRA in the pre-fusion form. An alanine scan was performed on the HRC domain using site-directed mutagenesis and the effect on fusion ability was assessed through syncytia formation in cell culture. Utilising lab-generated pre-fusion F models, a striking pattern was observed in that mutants that enhanced fusion aligned on one helical face, while some mutants that abrogated fusion lay on another. It is clear that HRC plays an important role in the fusion process and it is even postulated that HRC may engage the cellular receptor nucleolin, causing a small conformational change in HRC that is the trigger for fusion. The clustering of these residues and proposed mechanism of action provide opportunities that will direct further research and insights that may prove beneficial to anti-viral drug design.