Coronary arteries are blood vessels supplying oxygenated blood to the heart. Two coronary arteries, right and left, arises from the root of aorta. Root of aorta has three bulges known as sinuses of Valsalva. Coronary arteries arise from these sinuses. The sinus from which right coronary artery arises is known as right sinus and that from which the left arises, the left coronary sinus. The sinus from which no coronary artery arises is known as non-coronary sinus.
Left coronary artery branches into left circumflex (LCX) and left anterior descending (LAD) coronary arteries. Since both these are major branches, they are considered as separate vessels and the left main given a separate designation. LAD is often called the widow-maker artery because occlusion of proximal LAD causes a massive myocardial infarction which can very often be fatal. Sometimes the left main coronary artery (LMCA) trifurcates into LAD, LCX and a ramus intermedius.
LCX traverses the atrioventricular groove and gives off major branches known as obtuse marginals (OM). Left atrial circumflex is a branch of LCX, which supplies the sinus node in a few cases. When the LCX is dominant, it crosses the crux and gives off the posterior descending artery (PDA) and posterior left ventricular branches (PLV). LAD descends in the anterior interventricular groove. It gives off septal branches into the interventricular septum and diagonal branches which supply the lateral wall of the left ventricle.
Right coronary artery (RCA) is usually the dominant artery which crosses the crux, the junction of atrioventricular and interventricular grooves posteriorly. Hence the PDA and PLV often arise from the RCA. The first two branches of the RCA are the sinus node artery and the conus artery. RCA also gives off right ventricular branches and acute marginal branches. The atrioventricular nodal artery arises from the RCA if is dominant, usually from its genu where it becomes the PDA.