—Cyclic changes in the heart rate during breathing. Common in
children and often found in adults, as well. —The sinus node
sends out electrical signals faster than usual, speeding up the
heart rate. Sick Sinus Syndrome —The sinus node does not fire
its signals properly, so the heart rate slows down. Sometimes
the rate changes back and forth between a slow (bradycardia) and
fast (tachycardia) rate. Premature Supraventricular Contractions
or Premature Atrial Contractions (PAC) —A beat occurs early in
the atria, causing the heart to beat before the next regularly
expected heartbeat. Supraventricular Tachycardia (SVT),
Paroxysmal Atrial Tachycardia (PAT) —A series of early beats in
the atria speed up the heart rate. In paroxysmal tachycardia,
repeated periods of very fast heartbeats begin and end suddenly.
—Rapidly fired signals cause the muscles in the atria to
contract quickly, leading to a very fast, steady heartbeat.
—Electrical signals in the atria are fired in a very fast and
uncontrolled manner. Electrical