Variations in venous anatomy. Three dimensional volume rendered images from different CMR data-sets showing the anatomy of the cardiac veins. 4a – The AIV crossing over the LAD before a diagonal branch. 4b – The under-surface of the heart showing the PIV and a low LLV draining into the CS. 4c – A low LLV branch is seen. 4d – The CS is well demonstrated, but no tributaries are seen. High signal from pericardial fluid can be seen over the lateral wall. AIV = Anterior Interventricular Vein; PIV = Posterior Interventricular Vein; CS = Coronary Sinus; LAD = Left Anterior Descending Artery; LLV = Left Lateral Vein; OM = Obtuse Marginal Artery; RCA = Right Coronary Artery.