When faced with an infection or illness, one of the body’s primary defense mechanisms is a fever. A fever is an elevated body temperature, typically considered 100.4°F (38°C) or higher. Concurrently, you might notice your heart beating faster than usual. Your heart rate is simply the number of times your heart contracts per minute, often measured in beats per minute (bpm).
The Direct Relationship
An increase in heart rate is a common and expected response when you have a fever. This correlation is so consistent that a general rule of thumb exists. For every 1-degree Celsius (1.8-degree Fahrenheit) increase in body temperature, your heart rate can rise by approximately 10 beats per minute (bpm). This physiological adjustment is a natural part of your body’s response to an elevated temperature.
Understanding the Body’s Response
The heart rate increases during a fever due to several physiological mechanisms. When the body temperature rises, the metabolic rate increases, meaning the body works harder to fight off the infection. This heightened activity demands more oxygen and nutrients, which the heart must pump more rapidly to deliver to tissues. The immune system’s activation also plays a role in elevating heart rate.
Additionally, the body initiates vasodilation, a widening of blood vessels, to help release excess heat. This vasodilation can lead to a temporary drop in blood pressure, prompting the heart to beat faster to maintain adequate blood flow and pressure. The sympathetic nervous system, often called the “fight or flight” system, becomes more active during illness, releasing hormones that directly accelerate heart rate.
Other Influences on Heart Rate During Fever
While fever is a primary factor, other elements can influence your heart rate when you are unwell. Dehydration, common during illness due to reduced fluid intake, vomiting, or diarrhea, can cause the heart to beat faster to compensate for lower blood volume. Certain medications might also affect heart rate as a side effect.
Underlying medical conditions can further impact how your heart rate responds. Individuals with pre-existing heart conditions or anemia may experience a more pronounced heart rate increase. Age also plays a role; infants and older adults may exhibit different heart rate responses.
Recognizing Warning Signs
An increased heart rate with fever is generally a normal response, but there are situations where it warrants medical attention. Seek medical advice if your heart rate is extremely high for the degree of fever, or if it remains persistently rapid even after the fever begins to subside. Accompanying symptoms such as chest pain, significant shortness of breath, dizziness, or fainting are also concerning signs that require immediate evaluation. Signs of severe dehydration, like reduced urination or extreme thirst, should also prompt a medical consultation. Always consult a healthcare professional if you have concerns about your symptoms.