What signals the end of the cycle cycle?

it would be rhyolitic hope this

burning fossil fouls really decrease the carbon in the atmosphere so b

blood enters the heart through two large veins, the inferior and superior vena cava, emptying oxygen-poor blood from the body into the right atrium of the heart. as the ventricle contracts, blood leaves the heart through the pulmonic valve, into the pulmonary artery and to the lungs where it is oxygenated.