Possible causes of a rapid heartbeat include high blood pressure, an overactive or underactive thyroid gland, stress, electrical shock, and air pollution, according to Mayo Clinic. People who are having a heart attack or possess scarring of heart tissue from a previous heart attack also experience rapid heartbeat and require immediate medical attention.
Changes to the heart's structure and blocked heart arteries can cause the heart to beat rapidly, notes Mayo Clinic. People who drink too much caffeine or alcohol, smoke or abuse drugs may also experience rapid heartbeat. Certain herbal treatments, dietary supplements and prescription medications produce rapid heartbeat as well.
The heart may beat rapidly when people experience strong emotions such as fear, stress or anxiety, explains WebMD. People who engage in vigorous physical activity or experience hormonal changes due to perimenopausal stages, menstruation or pregnancy also cope with rapid heartbeat. A patient who has abnormal electrolyte levels or is dehydrated is likely to notice a rapid heartbeat.
People with healthy hearts commonly notice a resting heart rate of 60 to 100 beats each minute, according to Mayo Clinic. Athletes who are conditioned regularly experience a heart rate less than 60 beats each minute due to their training and the efficiency of the heart.