Bradycardia is the medical term for an abnormally slow heart rate. In healthy adults, the normal resting heart rate is about 70-80 beats per minute (athletes often have resting heart rates in the 60s and sometimes lower). In general, though, anything lower than about 60 beats per minute is considered bradycardia. In newborn babies, the normal heart rate is 120-160 beats per minute.
Bradycardia can ultimately cause poor circulation and starve the brain and other organs of oxygen and cause damage to those organs. Bradycardia is often the result of an overdose of certain depressant drugs like alcohol and tranquilizers.