Fast heart rate (more than 100 beats per minute) without obvious cause

A normal heart rate for a healthy adult is between 60 and 100 beats per minute. Heart rates of more than 100 beats per minute (tachycardia) can be caused by:

• 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 thedehydrationis treated, theheartrate usually returns to normal.
• Medicationside effects, especiallyasthma medications.
• Heavysmoking, alcohol, or too muchcaffeineor other stimulants, such asdiet pills. Stopping the use of tobacco, alcohol, caffeine, or other stimulants may help your heart rate return to normal.
• Cocaine,amphetamines, andmethamphetamines.

Babies and children younger than 2 years old have higher heart rates because their bodymetabolismis 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 diseaseor other medical conditions may sometimes cause a fast heart rate. A fast heart rate may causepalpitations,dizziness,lightheadedness, orfainting.Atrial fibrillationis the most common type of fast heartbeat. It causes the heart's upper chambers to beat irregularly, reducingbloodflow to the heart muscle and to the rest of the body. Atrial fibrillation increases your chance of having astrokeor ablood clotin thelungs(pulmonary embolism).

If you have heart disease,heart failure, or have had aheart attack, it is especially important to understand how serious a fast heart rate can be. This is especially true if it occurs with shortness of breath when you are resting or after mild exertion. Call your health professional if you have a sudden change in your usual heart rate or rhythm.