(1) The rhythm is regular with the R-R intervals constant and the P-P intervals constant.
(2) The atrial and ventricular rates are less than 60 beats per minute.
(3) The P wave is normal and upright with one P wave in front of every QRS complex.
(4) The P-R interval is constant between 0.12 and 0.20 seconds.
(5) The QRS complex measures less than 0.12 seconds.
(6) A heart rate of less than 60 beats per minute may indicate good physical conditioning if the individual is young and healthy.
(7) If the person is suffering from acute myocardial infarction (AM I), this heartbeat rate may indicate any one of the following: conduction system damage, increased parasympathetic tone, or possible toxic levels of certain cardiac drugs (digitalis, quinidine). If the heartbeat rate decreases to less than 50 beats per minute, the heart may not be able to pump enough fluid through the body's vital organs. Additionally, bradycardia leads to electrical instability in the ventricles, possibly resulting in ventricular arrhythmias.
NOTE: Males normally have a slower heart rate than females. Cardiovascularly healthy people may normally have a slow (less than 60 beats per minute) heart rate which also normally slows during sleep and rest. A slow heart rate is significant only if it is associated with MI or cardiovascular compromise.