During this time the two atria contract. Bicuspid and tricuspid valves open. But the semilunar eyelid remains closed. The pressure between the two atria increases. 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 0.1 seconds. The first 0.05 seconds of this is when the contraction is at its maximum. This is called dynamic phase. The second 0.05 seconds fades to fainter. This is called adynamic phase.