Left Coronary Artery (LCA)

The left coronary artery (LCA) is also known as the left main.
The LCA arises from the left coronary cusp.

The aortic valve has three leaflets, each having a cusp or cup-like configuration.
These are known as the left coronary cusp (L), the right coronary cusp (R) and the posterior non-coronary cusp (N).
Just above the aortic valves there are anatomic dilations of the ascending aorta, also known as the sinus of Valsalva. The left aortic sinus gives rise to the left coronary artery.
The right aortic sinus which lies anteriorly, gives rise to the right coronary artery.
The non-coronary sinus is postioned on the right side. 

Left coronary (LC), right coronary (RC) and posterior non-coronary (NC) cusp

 The LCA divides almost immediately into the circumflex artery (Cx) and left anterior descending artery (LAD).
On the down an axial CT-image.
The LCA travels between the right ventricle outflow tract anteriorly and the left atrium posteriorly and divides into LAD and Cx. 

LCA divides into LAD and Cx

On the image on the down we see the left main artery dividing into

• Cx with obtuse marginal branch (OM)
• LAD with diagonal branches (DB)

 On volume rendered images the left atrial appendage needs to be removed to get a good look on the LCA.

 In 15% of cases a third branch arises in between the LAD and the Cx, known as the ramus intermedius or intermediate branch.
This intermediate branche behaves as a diagonal branch of the Cx.