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Figure 1 Coronary sinus angiogram of a cadaveric human heart. This heart is splayed out in an anterior view to show the entire length of the atrioventricular venous ring on the left side of the heart. The dotted lines depict the near-equal segmental divisions along the horizontal (short) axis. The horizontal line extends from the coronary sinus ostium (origin of MV) to the point where the AV terminates into the great cardiac vein. Each of the segments are defined as follows: A = anterior segment; B = lateral segment; C = posterior segment. The segment refers to the region under the respective letters A, B, and C. Conventional branches are labeled as follows: AV = anterior interventricular vein; LV = lateral marginal vein; PV = posterior cardiac vein; MV = middle cardiac vein. This figure highlights the second- and third-order tributaries and collateral circulation.