Heart failure (HF) affects 1 million people in the UK with a similar number being undiagnosed. It carries a 50% mortality in 5 years and costs the NHS 2.5% of its annual budget (National Institute for Health and Clinical Excellence 2010). Atrioventricular node (AVN) conduction disturbance is common in HF and is associated with worse prognosis (Gervais et al. 2009; Olshansky et al. 2012). Three-month old male New Zealand rabbits (n=9, 2500-3000g) were anaesthetised with ketamine intramuscular injection and isoflurane inhalation. They underwent destruction of the aortic valve leaflets by repeated insertion of a catheter through the aortic valve (week 0) resulting in volume overload. Three weeks later banding of the abdominal aorta was performed by placing a silver clip (inside diameter 2.44mm) just above the right renal artery using the same anaesthetic schedule. This resulted in pressure overload. Echocardiography confirmed reduction of ejection fraction, and signs of HF were present prior to termination (week 8). Control animals underwent sham procedures. In vivo ECG recording showed significant prolongation of the PR interval, which remained significant after autonomic blockade. Interval immunofluorescence and Masson’s trichrome staining was used to construct anatomic “roadmaps” of the 18 AVN preparations. These were analysed using Matlab to study deformation. The tiny tissues of the AVN were dissected using laser-assisted microdissection (LMD). Transitional tissue (TT), the inferior nodal extension-including compact node- (INE), penetrating bundle (PB) and His bundle (HB), as well as atrial and right (RVS) and left (LVS) ventricular septal tissues were microdissected and mRNA extracted immediately. mRNA quantity and integrity were assessed using the NanoDrop ND-1000 spectrophotometer and Agilent 2100 bioanalyzer. We obtained RNA quantity of ≥100 ng with an average 260/280 RNA absorbance ratio of 1.84 (RIN 2.4-8.8), and studied 37 ion channels and connexins with quantitative RT-PCR. Values are expressed as means ± SEM, compared by t-test unless otherwise stated. Anatomically, HF hearts showed hypertrophy of the AVN at the PB and HB levels (combined HB+PB length 3.0 ± 0.186 mm (HF), 2.4 ± 0.231 mm (sham), P=0.04). The majority of transcripts were differentially expressed between working myocardium and the AVN conduction tissue (FDR<0.05). Steep ion channel gradients across the AVN itself (INE-PB-HB) were found for ANP, Kir3.1, HCN4, Kir2.1, Nav1.5 and TWIK-1 in both HF and sham. Kchip2 mRNA is significantly more abundant in RVS vs. LVS (FDR<0.05). In HF Cx43, HCN1 and Cav1.3 are down-regulated across all regions studied (P<0.05, 2-way ANOVA). Conversely, SUR2a, CLC-2, Navβ1 and Nav1.1 are up-regulated (P<0.05, 2-way ANOVA). Down-regulation of Cx43, Cav1.3 and HCN1 may help explain the AVN dysfunction and slowing of conduction in HF. Up-regulation of ANP in response to mechanical stress is well characterised in HF and our study supports this. We hypothesise that up-regulation of SUR2a, CLC-2, Navβ1 and Nav1.1 may act as a compensatory response to impaired AVN conduction.