What Causes A Rapid Heart Rate?

The heart is a part of the circulatory system, and is the organ responsible for circulating blood through the vessels to the lungs and body cells. The heart's pumping action can vary in both strength and rate, where stronger, faster heartbeats deliver more blood to the cells, while weaker or slower heartbeats deliver less blood. There are many possible reasons that heart rate could be elevated.

Pregnancy

One potential cause of an elevated heart rate is early pregnancy, though of course this applies only to women. During the early weeks of pregnancy---in many cases, even before a woman knows she's pregnant---the uterus begins to fill with blood. While blood volume will increase eventually to help meet an expectant mother's increased demands for blood supply, early in pregnancy, the blood volume has not yet changed to accommodate her embryo. As such, the heart circulates the existing blood volume faster, a feat accomplished through increased heart rate. While a pregnant woman's heart shouldn't race compared to normal, she'll nevertheless notice an elevated heart rate. In their book, "You: Having A Baby," Michael Roizen, M.D. and Mehmet Oz, M.D. note that pregnancy can add ten to fifteen beats per minute to a woman's heart rate.

Exercise

Everyone's heart works harder while they are engaged in exercise. Depending upon the intensity of exercise, this effect can vary from mild to quite significant. In fact, particularly strenuous efforts cause the heart to beat at nearly its maximal rate in an effort to supply body cells with plenty of blood. Dr. Gary Thibodeau, in his book "Anatomy and Physiology," explains that hard-working muscle cells require far more oxygen than resting muscle cells. Accommodations to exercise, therefore, include both more frequent, deeper breaths to increase oxygen intake, and elevated heart rate to increase the circulation of oxygenated blood.

Stress

The human body, like the bodies of animals, is designed to protect itself from threatened danger. Since physical threats generally necessitate that an animal or human either fight or run---both of which require significant physical effort---a threatened animal's body naturally responds by preparing to work hard. Heart rate increases dramatically to allow muscles plenty of oxygen. In "Human Physiology," Dr. Lauralee Sherwood explains that human bodies respond to psychological stress the same way they do to physical stress---increased respirations, rapid heart rate, and preparations to fight or run occur even when the threat is emotional. For this reason, many individuals experience elevated heart rates when faced with work- or home-related stress.