Fever and a rapid heartbeat are commonly experienced together. This article explores the physiological reasons behind this relationship, offering insights into why your heart might race when you have a fever.
What is Fever?
Fever is an elevation of the body’s core temperature beyond its normal range, typically considered above 100.4°F (38°C) when measured orally. It is not an illness in itself but rather a sign that the body’s immune system is actively working to combat an infection or illness. Common causes include viral infections such as influenza, bacterial infections, and inflammatory conditions.
What is Tachycardia?
Tachycardia refers to a heart rate that exceeds the typical resting rate, generally defined as over 100 beats per minute (bpm) for adults. This increased heart rate can be a normal physiological reaction, known as sinus tachycardia, occurring in response to everyday factors like exercise, stress, or excitement. However, tachycardia can also signal an abnormal heart rhythm unrelated to these usual triggers.
The Physiological Link Between Fever and Tachycardia
The body’s response to fever involves several integrated physiological mechanisms that result in an increased heart rate. When body temperature rises, metabolic processes within the cells accelerate, requiring more oxygen and nutrients. This prompts the heart to beat faster to circulate blood more efficiently.
Another contributing factor is the body’s effort to dissipate excess heat. Blood vessels near the skin’s surface dilate, increasing blood flow to the skin to release heat. The heart compensates for this increased superficial circulation by pumping more rapidly to maintain adequate blood pressure and ensure blood reaches other organs. Fever also activates the sympathetic nervous system, triggering stress hormones like adrenaline and noradrenaline. These hormones directly stimulate the heart, causing it to beat faster and with greater force.
Fever often leads to increased fluid loss through sweating, vomiting, or diarrhea, which can result in dehydration. Reduced fluid volume decreases the amount of blood circulating in the body. To compensate for this lower blood volume and maintain blood pressure, the heart works harder and beats faster. As a general guideline, for every 1°C (1.8°F) increase in body temperature, an adult’s heart rate typically rises by approximately 10 to 15 beats per minute.
When to Be Concerned
While a faster heart rate with fever is a common physiological response, certain signs indicate medical attention may be necessary. Prompt evaluation is warranted if a fever is accompanied by persistent chest pain, shortness of breath, dizziness, lightheadedness, fainting, severe weakness, confusion, or a racing heart that doesn’t subside as the fever improves.
A heart rate that remains very high, such as consistently over 130-140 bpm for an adult at rest, even with fever, or seems disproportionate to the degree of fever, should also prompt a medical consultation. Individuals with pre-existing heart conditions, chronic illnesses, or those who are very young (infants) or elderly may be more susceptible to complications and should seek advice. Additionally, a very high fever (e.g., above 103°F or 39.4°C) or one that lasts for several days without showing signs of improvement suggests the need for professional medical assessment.