During this time the atria are in two dilated states. Bicuspid and tricuspid cusps are closed. The pressure between the two atria decreases. As a result, blood containing CO2 enters the right atrium through the superior vena cava from the upper part of the body and the inferior vena cava from the lower part. At the same time O2-rich blood enters the left atrium through the pulmonary veins. The duration of this dasha is 0.7 seconds.