the control of the heartbeat! ________ _______ _________ initiates the heartbeat, which is not a conscious process. the ________ ____ controls the rate of the heart beat. a wave of extractions is sent, the _____ contracts, conducted to atrioventricular node and passed through the _______ to the ________, which contract. in the _______, chemoreceptors can detect more CO2 in the blood, which releases __________ which prepares for physical activity