| || | Heart and Circulatory Heart Rhythm problems A cardiac
arrhythmia is any abnormal heart rate or rhythm. InteliHealth
Medical Content What Is It? A cardiac arrhythmia is any abnormal
heart rate or rhythm. In normal adults, the heart beats
regularly at a rate of 60 to 100 times per minute, and the pulse
(felt at the wrist, neck or elsewhere) matches the contractions
of the heart's two powerful lower chambers, called the
ventricles. The heart's two upper chambers, called the atria,
also contract to help fill the ventricles, but this milder
contraction occurs just before the ventricles contract, and it
is not felt in the pulse. Under normal circumstances, the signal
for a heartbeat comes from the heart's sinus node, the natural
pacemaker located in the upper portion of the right atrium. From
the sinus node, the heartbeat signal travels to the
atrioventricular node, or "A-V node," (located between the
atria) and through the bundle of His (pronounced HISS - a series
of modified heart muscle fibers located bet