SYNTAX score is a scoring system for coronary lesions based on the online calculator available at www.syntaxscore.com. The online version is updated when new data from the follow up of SYNTAX trial is available. Latest downloadable version is 2.1 containing data from the three year SYNTAX trial results. Downloadable version is not automatically updated while the online version is. All lesions in both coronary territories in vessels of at least 1.5 mm diameter and of fifty percent or more severity should be scored. If tandem lesions are more than three times the diameter of the reference vessel apart, they should be scored as separate; otherwise as a single lesion. For the purpose of SYNTAX score, the vessel which gives rise to the posterior descending coronary artery is considered as the dominant vessel and there is no provision for co-dominance. Proximal, mid and distal right coronary artery segments are numbered 1-3 and posterior descending coronary artery as segment four. Posterior left ventricular branch (posterolateral branch) originating from the right coronary artery is numbered 16 and its branches and 16a, 16b, 16c, starting from proximal to distal. Left main coronary artery is segment 5. Proximal, mid and apical left anterior descending artery segments are numbered 6-8. 9 and 10 are diagonals. 11, 13 and 14 are for left circumflex coronary artery and its branches. Intermediate coronary artery is designated 12.