A resting heart rate (RHR) is the number of times your heart beats per minute while you are calm and not physically active. For most adults, a normal RHR falls within a range of 60 to 100 beats per minute. When you are sick, this number commonly increases beyond your normal rate. This elevated heart rate is a normal, temporary physiological response as your body fights infection.
How Illness Triggers a Faster Heartbeat
The most immediate cause for an elevated heart rate during illness is often a fever, which dramatically increases the body’s overall metabolic demands. The rise in body temperature requires the heart to work harder to deliver oxygen and nutrients to tissues. For every one-degree Celsius (1.8 degrees Fahrenheit) increase in body temperature, the heart rate typically rises by approximately ten beats per minute.
The body’s immune response also contributes by activating the sympathetic nervous system. When the immune system detects a threat, it releases chemical messengers called cytokines, which promote inflammation and directly stimulate the heart. This reaction triggers the release of hormones like epinephrine, causing the heart muscle to contract faster and increase blood output.
This increased circulation moves immune cells and proteins throughout the body more quickly to the site of infection. The accelerated heart rate ensures the body meets the heightened demand for resources while also helping to dissipate the heat generated by a fever. A faster heartbeat is often a sign that your body’s defense mechanisms are fully engaged.
Common Contributing Factors Beyond Fever
Even without a fever, other factors accompanying illness can push the heart rate higher. Dehydration is a frequent cause, especially when illness involves vomiting, diarrhea, or excessive sweating. When the body loses fluid, the total volume of circulating blood decreases. To compensate, the heart must beat faster to maintain adequate blood pressure and ensure organs receive necessary blood flow. Staying properly hydrated is important to reduce this strain.
Certain common over-the-counter medications can also directly stimulate the heart. Decongestants containing pseudoephedrine or phenylephrine constrict blood vessels to relieve nasal congestion. Because these ingredients are stimulants, they can inadvertently increase both blood pressure and heart rate.
Finally, the stress of feeling unwell and poor sleep contribute to an elevated resting heart rate. Worry or discomfort keeps the body in a state of heightened anxiety. This mental and physical stress activates the nervous system, adding to the heart’s workload.
Recognizing When a High Heart Rate Needs Medical Attention
While an elevated heart rate is usually a normal part of being sick, specific signs indicate a need for medical evaluation. Seek guidance if your resting heart rate remains consistently above 120 or 130 beats per minute. It is particularly concerning if the heart rate does not decrease after a fever has broken or underlying symptoms have been managed.
Immediate medical care is necessary if a fast heart rate is accompanied by severe symptoms suggesting cardiovascular distress:
- Chest pain or significant discomfort.
- Severe shortness of breath.
- A feeling of confusion.
- Sudden dizziness or lightheadedness.
- Feeling as though you might faint.
A disproportionately high heart rate compared to a fever may signal an underlying complication, such as a severe systemic infection like sepsis. In rare cases, the infection may directly affect the heart muscle, a condition called myocarditis, which requires urgent diagnosis.