The arterial supply is  by the right and left coronary arteries. In the event of sudden block of one artery the area of myocardium supplied by that artery undergoes infarction.  

 Right coronary artery

 Right coronary artery arises from the anterior aortic sinus. Just before its termination it gives off the posterior interventricular branch that runs downwards, forwards and to the left in the posterior interventricular groove. The branches of the right coronary artery are, branches to SA node, branches to right atrium and right ventricle, right marginal artery, posterior interventricular branches and branches to AV node. It is to be noted that the right coronary artery supplies the right atrium, right ventricle and conducting system of the heart.  

 Left coronary artery  

 The left coronary artery arises from the left posterior aortic sinus. It divides into anterior interventricular branch (left  anterior descending -LAD) and circumflex artery. The left coronary artery supplies left ventricle, left atrium, anterior two third of the I.V. septum and adjacent part of the right ventricle.  The branches of the left coronary artery: Anterio interventricular artery (LAD) and  Circumflex artery which is considered to  be the continuation of the left coronary artery. It gives rise to the left obtuse marginal arteries  and also few branches for the supply of the posterior surface of the left atrium and left ventricle. Anterior interventricular branch of the left coronary artery(LAD) has septal branches and diagonal branches and  supplies the left anterior surface of the left ventricle including the apex, adjoining part of the left ventricle and anterior two-third of the IV septum. The LAD runs along the anterior interventricular sulcus, turns around the inferior border of the heart and anastamoses with the posterior interventricular branch of the right coronary artery.