Detailed descriptions of cardiacgeometry and architecture are necessary for examining andunderstanding structural changes to the myocardium that are theresult of pathologies, for interpreting the results ofexperimental studies of propagation, and for use as athree-dimensional orthotropically anisotropic model for thecomputational reconstruction of propagation during arrhythmias.Diffusion tensor imaging (DTI) provides a means to reconstructfibre and sheet orientation throughout the ventricles. Wereconstruct and quantify canine cardiac architecture in selectedregions of the left and right ventricular free walls and theinter-ventricular septum. Fibre inclination angle rotates smoothlythrough the wall in all regions, from positive in the endocardiumto negative in the epicardium. However, fibre transverse and sheetangles show large variability in basal regions. Additionally,regions where two populations (positive and negative) of sheetstructure merge are identified. From these data, we conclude thata single DTI-derived atlas model of ventricular architectureshould be applicable to modelling propagation in wedges from theequatorial and apical left ventricle, and allow comparisons toexperimental studies carried out in wedge preparations. However,due to inter-individual variability in basal regions, individual(rather than atlas) DTI models of basal wedges or of the wholeventricles will be required.