Which of the following statements is TRUE about heart rate and exercise? A. It is best to exercise your heart as hard as possible.

B. Maximum heart rate can be calculated by taking 220 minus your age.

C. Your recommended exercise heart rate is 30% of your maximum heart rate.

D. All of the above are true statements.

Check all that occur during ventricular systole. a. the av valves open to allow blood to enter the ventricles from the atria. b. the av valves open to allow blood to enter the ventricles from the atria. c. the semilunar valves remain closed throughout systole to prevent backflow of blood into the ventricles. d. the semilunar valves remain closed throughout systole to prevent backflow of blood into the ventricles. e. the semilunar valves open to allow blood to flow into the large arteries. f. the semilunar valves open to allow blood to flow into the large arteries. g. the av valves close to prevent backflow of blood into the atria.