1. During the atrial systole, the atrial muscles _______.   relax   contract   2. Plasma is a constituent of blood.   True   False   3. During the atrial systole, the openings of the pulmonary vein and the vena cava are _______.   closed   open   4. The _______ of the heart pumps the blood up to the lungs only.   right ventricle   left ventricle   left auricle   right auricle   Hint Half-n-half Clue   5. The left auricle of the heart receives _______ blood from the lungs.   oxygenated   deoxygenated   6. With reference to the heartbeat, the word 'systole' refers to a relaxation phase whereas the word 'diastole' refers to a contraction phase.   True   False   7. The process of circulation of blood in the heart begins with the _______ of the auricles of the heart.   relaxation   contraction