We gather together again from both sides of the lungs in the left atrium. This is really just a rest stop as we wait to go into the left ventricle. The AV valve separating the left atrium and the left ventricle is a bicuspid valve this time because it's made up of just two sections.
The contraction of the left atrium actually happens at the same time as the contraction of the right atrium over on the other side.
