INTRODUCTION: Brugada Syndrome (BrS) is an inherited arrhythmia syndrome characterised by ST-segment elevation in the right precordial ECG leads and is associated with an increased risk of sudden cardiac death. We identify and characterise a novel SCN3B variant encoding the regulatory β3-subunit of the cardiac voltage-gated sodium channel, Na METHODS AND RESULTS: A 54-year-old Caucasian male presented with palpitations and dizziness. An ECG identified a spontaneous type 1 BrS pattern and review of his medical records revealed a prior type 1 BrS ECG. Next generation sequencing of a BrS risk panel of genes identified a novel SCN3B deletion (c. c412-414, p.T138Del) yielding a single amino acid deletion. No other pathogenic variants were identified. Using site-directed mutagenesis we made the β3-ΔT138 variant and examined structural and functional effects in a heterologous system. Computational predictions together with circular dichroism spectroscopy showed highly localised structural perturbations with minimal effect on the gross protein architecture. Biotinylation, co-immunoprecipitation and surface cross-linking experiments identified normal β3 surface expression and interaction with Na CONCLUSION: A novel BrS associated SCN3B deletion introduced minimally disruptive structural perturbations to the regulatory β3-subunit of Na