During this time the two ventricles are in dilated or relaxed state. Bicuspid and tricuspid cusps are open. But the semilunar eyelid remains closed. The pressure between the two ventricles decreases. As a result, blood containing CO2 enters the right ventricle from the right atrium and blood containing O2 enters the left ventricle from the left atrium. The duration of this dasha is 0.5 seconds.