iRzilla

Hello, I am 9th grade biology student working on a presentation on the heart. I was wondering if you guys could help me understand the basic mechnics of the heart. I also have to talk about what happens when an arterial valve fails and what arythmia is. I am trying to find resources online, so if you guys have any good websites it would be awesome if you could post them here! And last thing, could you guys just describe in your own simple words? Thanks so much!