Vascularity of the heart
In keeping with medical drawings this morning at work I swiped a little heart model out of the exam room. Later I might attempt a Netter heart but the model is a lot simpler. I really like drawing this medical stuff as it blends my work as a medical practice manager with liking to draw (at work. Goofing off).
Here is the model I used. It has a little card in the back with the identifiers.