When the body encounters an infection, it undergoes physiological adjustments to combat invading pathogens. An increase in heart rate is a common observation during illness. This elevated heart rate reflects the heightened demands placed on various bodily systems as the body fights the infection. Understanding these processes helps explain why your heart beats faster when you are unwell.
The Body’s Overall Response to Infection
When a pathogen enters the body, the immune system activates its defenses. This initial response, known as innate immunity, is a rapid, non-specific reaction designed to contain the threat. Immune cells like neutrophils and macrophages deploy to the infection site, where they engulf and destroy pathogens.
The immune response involves the release of chemical messengers called cytokines, which signal inflammation. This inflammation, characterized by increased blood flow and the recruitment of more immune cells, is a natural part of the healing process. The body’s metabolic rate also increases to support the heightened activity of immune cells. A common manifestation of this increased metabolic activity is fever, where the body’s temperature rises. Elevated temperatures can inhibit microbial growth and accelerate repair processes.
How Infection Influences Heart Rate
The physiological changes accompanying an infection directly influence heart rate. When body temperature rises due to fever, the metabolic rate increases by approximately 10-13% for every 1°C (1.8°F) elevation. This heightened metabolic demand requires more oxygen delivery to tissues, prompting the heart to pump faster to meet increased circulatory needs. This relationship, known as Liebermeister’s rule, suggests that for every degree Celsius increase in body temperature, heart rate typically rises by about 10 beats per minute.
Inflammation also plays a direct role in elevating heart rate. The release of inflammatory cytokines can directly affect how the heart functions. These mediators contribute to a systemic inflammatory response that can stress the cardiovascular system, leading to a faster heartbeat.
Fever often causes peripheral vasodilation, a widening of blood vessels to help dissipate heat, which can lead to a relative decrease in circulating blood volume. The heart compensates by increasing its rate to maintain adequate blood pressure and ensure proper blood flow to tissues. The sympathetic nervous system, responsible for the body’s “fight or flight” response, is activated during infection, releasing hormones like epinephrine and norepinephrine that directly stimulate the heart to beat faster and stronger.
When a Fast Heart Rate Signals Concern
While an increased heart rate is a normal physiological response to infection, certain signs may indicate a more serious underlying issue. A heart rate disproportionately high for the degree of fever, or one that remains very elevated even as other symptoms improve, warrants attention. For example, a persistent heart rate above 100 beats per minute in an adult, especially without significant exertion, suggests a need for medical evaluation.
Other concerning symptoms that may accompany a fast heart rate include shortness of breath, chest pain or discomfort, or dizziness. If these symptoms occur, or if there is confusion, agitation, or a significant drop in blood pressure, it may suggest complications such as sepsis or other cardiovascular strain. In such situations, seeking prompt medical attention is advisable to ensure a proper diagnosis and appropriate treatment.