If
left on its own, the heartbeat is between 110 and 120 times
in one minute. This can be useful during exercise, but it is
too fast for an adult person at rest. This means the heart
has to be restrained by the brain so
that it can beat at a rate between 65 and 75 beats per
minute during rest in order to conserve energy and also
preserve the heart itself from exhaustion. This is why
cardiac vagal tone is very important when a person is
resting. A strong and efficient heart requires a greater
degree of restraint than a weak and inefficient heart.
