What would happen if the heart did not pump faster durring exercise?
You would use up all of your oxygen supply. The demand on the heart would cause a hypoxic episode. You would either pass out or have a critical dysrrhythmia...and possible die.
You wouldn't be able to do the exercise and it could be quite possible for your body to shut down, because your body is pumping the extra blood you need to be able to do the exercise.
When you're out of physical shape you heart tends to pump harder when you performing activities.When your body is use to strenuous physical activities, you're heart does not work as hard because it's accustom to it.