A resting heart rate is considered high if it falls above 100 beats per minute, the upper range of a normal heart rate, although some patients may choose to be evaluated for possible treatment if the heart rate is consistently above 80 or even 70 beats per minute. This rate can be caused by a number of things, from an infection somewhere in the body to dehydration or anxiety. While having a high resting heart rate for infrequent and short periods of time, such as during a fever, is not necessarily dangerous, it should be evaluated and treated by a doctor if it remains consistently above normal for an extended time because it increases the risk of problems such as heart attacks and strokes. Some people with a chronically high heart rate may need to be put on medication for the condition, but in many cases, the rate can be lowered simply by pinpointing and removing or treating the specific cause.
The resting heart rate is often the result of the body's reaction to relatively normal physiological reactions. Stress, anxiety, and dehydration can all be causes for a high rate. Being out of shape physically can make the heart work harder to maintain a normal level of circulation, causing it to beat faster. Counterintuitively, overtraining, or exercising too much, can also have the same effect.
On many occasions, a high resting heart rate may be the result of food, beverages, or drugs that have been consumed. Drinking caffeinated soft drinks, taking pills, such as energy pills or diet pills that contain caffeine and other stimulants, or taking other forms of stimulants can increase the resting heart rate significantly. Additionally, smoking and drinking large amounts of alcohol can both contribute to a high rate. In some cases, an individual can have a reaction to a medication he or she is taking for other reasons, which may also raise the heart rate above normal.
Sometimes, however, a high resting heart rate can indicate the presence of a disease or other health problem. Heart defects, heart disease, blood loss or anemia, and high blood pressure can all potentially cause a high resting heart rate. Fever and infection also increase the heart rate, so that the body can increase the blood supply to the infected areas and boost healing. Hyperthyroidism, when the thyroid gland functions at above normal capacity, also tends to increase the rate.