A noticeable acceleration of the heart rate, known medically as tachycardia or felt as palpitations, is a common symptom when the body fights off infection. This “racing heart” often accompanies viral or bacterial illnesses like the flu or a cold. While unsettling, it usually signals that the body’s internal systems are actively engaged in combating the invading pathogen. Understanding these physiological processes helps distinguish a normal defense mechanism from a symptom requiring medical attention.
How Illness Triggers a Faster Heart Rate
The body’s natural response to an infection involves several interconnected processes that increase the heart’s workload and speed. When a fever develops, the elevated body temperature directly increases the metabolic rate of all tissues. This heightened metabolism demands a greater supply of oxygen and nutrients, which the heart must pump faster to deliver. For every one degree Celsius (1.8 degrees Fahrenheit) rise in body temperature, the heart rate can increase by approximately 10 beats per minute.
The presence of a pathogen also initiates an immune response that activates the sympathetic nervous system, known as the “fight or flight” mechanism. Inflammatory cytokines, signaling proteins released by immune cells, stimulate the release of stress hormones like adrenaline and noradrenaline. These hormones act directly on the heart muscle, causing it to beat with greater force and increased frequency. This sympathetic activation mobilizes the body’s resources to fight the infection.
Many illnesses involve fluid loss through sweating, vomiting, or diarrhea, which can lead to dehydration. When the body is dehydrated, the total volume of blood circulating through the vessels decreases. To compensate for this lower blood volume and maintain adequate blood pressure and circulation to the vital organs, the heart must pump more times per minute. The heart is essentially working harder to circulate a smaller amount of fluid, which results in a visibly faster pulse.
The Influence of Common Cold and Flu Medications
Medications commonly taken to manage cold and flu symptoms can independently contribute to a racing heart, compounding the effect of the illness. Many over-the-counter nasal decongestants contain ingredients like pseudoephedrine or phenylephrine. These compounds are classified as sympathomimetics, meaning they mimic the effects of the sympathetic nervous system.
Decongestants work by stimulating alpha-adrenergic receptors, which causes vasoconstriction, or the narrowing of blood vessels in the nasal passages, helping to clear congestion. However, when taken orally, this effect is systemic, meaning it constricts blood vessels throughout the body, including those that regulate blood pressure. This widespread vasoconstriction increases resistance to blood flow, forcing the heart to pump harder to push blood through the narrowed vessels, leading to an elevated heart rate.
In healthy adults, pseudoephedrine may cause only a small increase, but this effect becomes more pronounced when the body is already stressed by illness. Additionally, many multi-symptom cold and flu preparations contain caffeine, a central nervous system stimulant. Caffeine further stimulates the heart, amplifying the risk of palpitations when combined with the decongestants already present.
Recognizing Warning Signs and When to Consult a Doctor
While an elevated heart rate is a typical sign of illness, certain accompanying symptoms signal a transition from normal to potentially dangerous. A rapid heart rate, or one that feels irregular, should prompt immediate medical evaluation if accompanied by:
- Severe shortness of breath or difficulty breathing.
- Chest pain or significant pressure in the chest.
- Signs of poor brain perfusion, such as lightheadedness, severe dizziness, confusion, or fainting (syncope).
A resting heart rate that remains consistently above 100 beats per minute, even after a fever has been reduced with medication and you have rested, warrants a conversation with a healthcare professional. This persistence suggests the tachycardia may not be solely a fever response.
Individuals with pre-existing heart conditions, such as atrial fibrillation, heart failure, or coronary artery disease, should consult their physician much sooner than healthy individuals. For these patients, the additional stress of illness and a sustained rapid heart rate can lead to complications like heart failure decompensation or an irregular rhythm. To manage the temporary increase, ensuring adequate fluid intake, particularly with electrolyte solutions, and prioritizing rest are simple actions that can help reduce the strain on the heart.