Question 1
The heart's valves open and close in response to changes in
◦ the heart's pacemaker.
◦ pressure.
◦ sodium and potassium concentration.
◦ oxygenation.
Question 2
Heart valves serve what purpose?
◦ They prevent backflow of blood.
◦ They control the heart's electrical signals.
◦ They prevent blood from flowing forward.
◦ They prevent oxygenated blood from flowing through the coronary arteries.