Cardiac anatomy from right to left

Right atrial appendage

The right atrial appendage is the trabecularized part of the right atrium.
It partially covers the atrioventricular groove and the right coronary artery that runs in it.
Characteristically, it is flat and triangular in shape and contains small muscular bundles which run parallel to the atrium itself. 

Axial (left) and 3D-reconstructions (right) of the heart demonstrating the right atrial appendage (blue arrows). Ao=aorta, LA=left atrium