Final answer:
An abnormally slow heart rate, known as bradycardia, is defined as having fewer than 60 beats per minute and may require treatment if accompanied by certain symptoms.
Step-by-step explanation:
An abnormally slow heart rate, fewer than 60 beats per minute, is called bradycardia. This condition may occur in well-trained athletes or can be a sign of a heart conduction system problem. If bradycardia is accompanied by symptoms such as weakness, lightheadedness, or fainting, it may indicate that the heart isn't supplying enough oxygen-rich blood to the body. In such cases, a pacemaker might be necessary. On the other hand, a rapid heart rate above 100 beats per minute when at rest is known as tachycardia, which can be caused by stress or underlying health conditions and may require medication or other treatments depending on its cause.