how fast is a heartbeat
Heart rates of more than 100 beats per minute (tachycardia) can be caused by: 1  Exercise or stress. 2  Illnesses that cause fever. 3  Dehydration. 4  Medicine side effects, especially asthma medicines. 5  Heavy smoking, alcohol, or too much caffeine or other stimulants, such as diet pills. 6  Cocaine, amphetamines, and methamphetamines.