Answer:
The right auricle opens into the right ventricle, this opening is guarded by the tricuspid valve (having three cusps or flaps). Similarly, the opening between the left auricle and the left ventricle is guarded by the bicuspid valve (having two cusps or flaps). These valves regulate the flow of blood in one direction i.e., from auricles into the ventricles.
The blood flows from the right ventricle into the pulmonary artery and from the left ventricle into the aorta (the largest artery). The flow of blood from the ventricles into these two arteries is also regulated by valves. These valves resemble a half moon, hence they are called semi-lunar valves. These valves are present at the opening where the pulmonary artery and aorta leave the right and left ventricles respectively. They ensure that the blood does not flow back into the ventricles.