Introduction: Sinus node (SN) dysfunction is a common clinical condition that is accounted for 50% of permanent pacemaker implantation. In order to examine the value of the goat as a model of human SN function and dysfunction we examined the structure of the SN and the surrounding right atrium in this species. Method: Right atria were harvested from 4 humanely killed goats. Under 3% Isoflurane anaesthesia, two of the 4 animals underwent an incremental protocol of epicardial SN ablation, sufficient to cause at least a 50% fall in heart rate, in order to determine the functional extent of the SN. All preparations were frozen, serially sectioned at 1 mm intervals and stained for histology using Masson trichrome technique. The extent and morphology of the native and ablated SN were determined. For verification of the histology, immuno-staining for Connexin43 (Cx43; a negative marker for the SN) and Na/Ca exchanger (NCX, a membrane-bound ion channel protein; positive marker for of all cardiomyocytes) was used on selected tissue sections. Images were taken with light and confocal microscopy. Results: The goat SN was located in the intercaval region (ICR) parallel to the crista terminalis (CT) and extended 2/3 of its length in the long axis. In the short axis, the centre of the SN occupied the full thickness (2mm) of the intercaval region (panel A). The SN, as in other species, consisted of cells which were small, lightly stained (compared to atrial myocytes) and embedded in a network of connective tissue (panel B, C) 1,2. All myocytes expressed NCX but not Cx43 unlike atrial myocytes. We also observed a transitional zone (TZ), (panel D) arising on the endocardial side of the CT (Panel A) which extended caudally beyond the SN. The morphology of TZ was intermediate to nodal and atrial tissue; conaining atrial as well as nodal cells..In addition, TZ contained an intermediate cell-type which histologically was similar to atrial myocytes, but lacked expression of Cx43; similarly to the novel paranodal area recently described in the human heart3 . In the experimental goats, the size and location of the ablated area corresponded to that of the healthy SN in the control group, but it spared an area caudal to the SN and did not involve the TZ. Conclusions: The SN in the goat is associated with an extensive adjacent region of transitional cells, similar to that recently described in the human. The natural function of this region is currently unknown but may provide a useful target for novel methods of “biological pacemaking” currently in development.