- Exercise or stress. This fast heart rate usually returns to normal range (60 to 100 beats per minute) with rest and relaxation.
- Illnesses that cause fever. When the cause of the fever goes away, the heart rate usually returns to normal.
- Dehydration. When the dehydration is treated, the heart rate usually returns to normal.
- Medicine side effects, especially asthma medicines.
- Heavy smoking, alcohol, or too much caffeine or other stimulants, such as diet pills. Stopping the use of tobacco, alcohol, caffeine, or other stimulants may help your heart rate return to normal.
- Cocaine, amphetamines, and methamphetamines.
Babies and children younger than 2 years old have higher heart rates because their body metabolism is faster. Heart rates decrease as children grow, and usually by the teen years the heart rate is in the same range as an adult's.
A new fast heart rate may be caused by a more serious health problem. Heart disease or other medical conditions may sometimes cause a fast heart rate. A fast heart rate may cause palpitations, dizziness, lightheadedness, or fainting. Atrial fibrillation is the most common type of fast heartbeat. It causes the heart's upper chambers to beat irregularly, reducing blood flow to the heart muscle and to the rest of the body. Atrial fibrillation increases your chance of having a stroke or a blood clot in the lungs (pulmonary embolism).