According to the American Heart Association, heart rate varies from person to person. What can be considered dangerously low for one person may be normal for another. A person's normal heart rate depends on a number of factors, including age and physical condition.
The Mayo Clinic states that an average person's resting heart rate falls between 60 and 100 beats per minute. However, Web MD adds that a lower than average heart rate is not necessarily a sign of a problem. Athletes and healthy young adults often have low heart rates.
According to WebMD, aging, medications, and certain heart diseases and infections can all cause low heart rates. Symptoms of a dangerously low heart rate include dizziness, shortness of breath, exhaustion, chest pain and difficulty concentrating.