(full 3 megapixel phone camera pics below)
Left Ventricle. The "stringy" looking things on the right-ish in the photo is the bicuspid (mitral) valve. It also has a much thicker muscle mass on this side of the heart, because the left side pumps blood from your lungs all throughout your body.
Right Ventricle. This side has a smaller muscle mass, because all it does is send blood from your body to the lungs (which will come back through the left ventricle).
It was a preserved sheep's heart. The heart weighed a nice 448.5 grams. I also did pretty much all the work, I chose the one guy who would just talk with other people the whole time and probably get a low participation grade because God knows I hate it when other people mess up the lab for me.
We've dissected loads of other things, like a spiny dogfish shark (which I already did in 6th grade), a frog (typical), perch, earthworms, squids, and more.