Number of
heart beats for minute. The
usual resting adult heart beats regularly at an
average course of 60 times for minute. (young children's hearts
beat faster). The
speed of the heartbeat (heart rate) is governed by the
speed of
electrical signals from the
pacemaker of the heart, the sa knot, situated in the
right atrium (upper
chamber of the heart). The
electrical signals from the sa
knot travel across the
atria and
reason these
two upper heart chambers to contract, delivering
blood into the lower
heart chambers, the ventricles. The
electrical signals then
pass through the av
knot to
reach the ventricles. Electrical signals
achievement the
ventricles reason these chambers to contract, pumping
blood to the
rest of the body, generating the pulse. During rest, the
speed of
electrical signals originating from the sa
knot is slow, so the
heart beats slowly. During exercice or excitement, the
speed of signals from the sa
knot increases, and the heartbeat quickens.