A person’s resting heart rate (RHR) is the number of times their heart beats per minute while at rest, typically measured after a period of calm. It is a common physiological observation that RHR often increases when the body is fighting an illness. This elevation in heart rate is generally a normal and expected response as the body works to combat infection or inflammation.
The Body’s Response to Illness
When you become ill, your body initiates physiological responses to fight pathogens and restore health. These responses directly influence your heart rate, causing it to rise above its typical resting level.
An elevated body temperature, or fever, is a common symptom of illness. For every 1 degree Celsius (1.8 degrees Fahrenheit) increase in body temperature, the heart rate typically rises by approximately 10 beats per minute, a relationship sometimes referred to as Liebermeister’s rule. This occurs because a higher body temperature increases the metabolic rate, meaning the body needs more oxygen and nutrients delivered to its tissues. The heart compensates by pumping faster to meet this increased demand and maintain adequate blood flow. Fever also triggers the sympathetic nervous system, releasing catecholamines like epinephrine and norepinephrine, which directly increase heart rate.
The body’s immune response to infection involves the release of signaling molecules called cytokines. These inflammatory cytokines, such as interleukin-1 (IL-1), interleukin-6 (IL-6), and tumor necrosis factor-alpha (TNF-α), can directly impact the cardiovascular system. Cytokines can activate the sympathetic nervous system, leading to an increased sympathetic outflow throughout the body, which then elevates heart rate. They can also cause changes in the heart’s electrical conductivity, contributing to a faster heartbeat.
Dehydration, often a consequence of illness due to fever, vomiting, or diarrhea, also contributes to an increased heart rate. When the body loses more fluids than it takes in, the total volume of blood circulating through the body decreases. To maintain blood pressure and ensure that oxygen and nutrients reach all tissues, the heart must work harder and pump faster. This compensatory mechanism is the heart’s way of trying to maintain circulation despite reduced fluid volume.
When to Be Concerned and What to Do
A moderate increase in resting heart rate during illness is an expected physiological response and generally resolves as the illness subsides. For most adults, a normal resting heart rate ranges between 60 and 100 beats per minute, though it will likely be higher when sick. This temporary elevation indicates your body is actively working to recover.
There are warning signs that should prompt medical attention if experienced alongside an elevated RHR during illness. Seek immediate medical advice if you experience any of the following:
Your RHR is consistently very high (e.g., above 100-120 bpm at rest, depending on your usual baseline and other symptoms).
Shortness of breath.
Chest pain.
Dizziness or fainting.
Confusion.
Persistent light-headedness or a racing, pounding heartbeat (palpitations) that does not improve.
Your heart rate remains elevated long after other illness symptoms have improved.
While recovering from an illness, several self-care measures can support your body’s natural healing process and help manage your heart rate. Prioritize rest to allow your body to conserve energy for fighting the infection. Staying well-hydrated is also important; drink plenty of fluids like water and electrolyte-rich beverages to replenish any fluid loss from fever, vomiting, or diarrhea. If appropriate, following medical advice regarding fever reducers, such as acetaminophen or ibuprofen, can help lower body temperature and, in turn, may help reduce heart rate.