There are many factors that affect your heart rate. The heart rate can speed up or slow down because of stress, exercise, medication, trauma or illness. Even breathing can cause slight fluctuations in heart rate. Most of the time a person does not really think about changes in his heart rate. Only when the change is significant does he become aware, and possibly concerned, depending on the effect.
For many people there is a natural occurrence during respiration; the heart rate slows ever so slightly during inspiration. When you breathe in, you might notice your heart rate slow down and then immediately return to normal.
Donna D. Ignatavicius, MS RN, and M. Linda Workman, Ph.D, authors of "Medical-Surgical Nursing - Critical Thinking for Collaborative Care," explain that part of the human response to psychological stress is an increase in heart rate. Emotional stress causes the same effects as physical stress. Anxiety and fear cause the release of hormones that make the heart pump faster and harder to provide muscles with necessary energy for self defense or escape.
Hard work and exercise increase the heart rate of a healthy heart. To meet the body's demand for more oxygen, the heart beats faster and harder. In an unhealthy heart, the increased demands for oxygen may fatigue the heart and cause bradycardia, or a slow heart rate.
Vagal stimulation involves special sensors in the body that are attuned to blood pressure changes. When a person bears down to have a bowel movement, deliver a baby or lift something very heavy, the increased pressure in the body signals the heart to slow down its rate.
Prescriptions, over-the-counter medications, herbal supplements, diet aids and street drugs can affect the heart rate. Stimulants like caffeine, ephedrine or cocaine can cause an increased heart rate. Beta blockers and digitalis preparations can slow down the heart rate.
Barbara McLean, CCNP, and Janice Zimmerman, M.D., authors of "Fundamental Critical Care Support," discuss how fever and septic shock can affect the heart rate. A fever places an increased metabolic demand on the body, and the heart rate increases to meet oxygen demands. When an infection overcomes the body's defense system, the illness becomes systemic, the person is said to be septic and shock ensues. As the body loses its battle against the infection, the circulatory system collapses and heart rate falls. Other disease processes such as thyroid disease, anemia (low blood count) and trauma are factors that affect the heart rate, either increasing or decreasing it.
The American Heart Association explains that heart disease from atherosclerosis (plaque buildup in arteries) can lead to a heart attack, heart failure or irregular heart rhythms called arrhythmias. Arrhythmias can affect the heart rate, making it too fast or too slow. Heart muscle damage can also happen from viral and bacterial illness and drug use.