The coronary vasculature is characterized by highly asymmetric diameters at bifurcations which may be an important determinant of flow distribution. In order to facilitate accurate reconstruction of the coronary network for hemodynamic analysis, we introduce a statistical data-set of the diameter asymmetry at bifurcations based on morphometric data of the porcine coronary arterial and venous trees. The bifurcation asymmetry data were represented by the diameter ratio of the daughters relative to mother vessel and by an area expansion ratio (AER) at each bifurcation. A novel Asymmetry Ratio Matrix (ARM) was introduced to describe the diameter asymmetry of daughters to mother vessels. The relations between AER and flow velocity, and ARM and flow distribution were considered. The results indicate that the ratio of large daughter to mother vessel has a minimum value at order 5 (mean diameter of about 70 µm) while the ratio of small daughter to mother vessel decreases monotonically with increase in order number. The AER was found to be fairly uniform for larger vessels and to increase from order 5 towards the capillaries. At order 5, we observe a transition in asymmetric bifurcation pattern that may mark a hemodynamic transition from transmural to perfusion sub-networks. The functional implications of these structural transitions are considered.