Okay, since my last post was obviously botched, I'm going to try again. This time I won't be including the link I posted before. My best advice would be to look up a description of how blood flows through the heart. This video should provide a good example:
(The video that made Reznor my hero.)
If something in this post needs to be changed, please change it instead of flat-out deleting it. I'm posting this to help someone out, so if I need to fix something, just let me know and I will.