Panel A, subpanel i shows the relative percentages of fat, fibrosis and myocardium in the PLA vs. LAA in HF dogs. Panel A, subpanel ii shows the heterogeneity of fat, fibrosis and myocardium in the PLA and LAA of HF dogs. Panel B, subpanels i - iv show individual sections (4X) from the PLA (subpanels i and iii) and LAA (subpanels ii and iv) respectively, highlighting that: a) there is significantly more fat in the PLA than the LAA and b) fibrosis, fat and myocardium are all more heterogeneously distributed in the PLA than the LAA. In addition, subpanel i demonstrates a typical nerve trunk in the PLA.