Most people think of influenza or the flu as a respiratory infection that only affects the nose, throat, and lungs. But influenza can affect much more than the respiratory system. The flu can place additional stress on the heart and increase the risk of serious cardiovascular problems, particularly in people who already have heart disease.
Research has found a clear association between influenza infection and events such as heart attack, heart failure, abnormal heart rhythms, and stroke.
This does not mean that everyone who gets the flu will develop a heart problem. In this article, Begin Health Life explains on how influenza can create conditions that make cardiovascular complications more likely, especially in people with existing risk factors.
How Can the Flu Affect the Heart?
The connection between influenza and heart health is more complicated than the flu virus simply "attacking" the heart.
Influenza triggers an immune response throughout the body. This causes inflammation and can increase the body's demand for oxygen and energy in metabolism while a person is fighting the infection. At the same time, fever, rapid heart rate, dehydration, reduced oxygen levels, and changes in blood clotting can place additional stress on the cardiovascular system.
For someone with healthy arteries and a healthy heart, the body may tolerate this temporary stress reasonably well. But someone with narrowed coronary arteries, heart failure, or another cardiovascular condition may have less reserve.
This is one reason flu and heart disease can be a particularly concerning combination.
Why Does Flu Increase Heart Attack Risk?
A heart attack usually occurs when blood flow through a coronary artery becomes severely blocked, often because a blood clot forms over a ruptured cholesterol-containing plaque. Influenza may contribute to this process in several ways.
1. Inflammation can destabilize artery plaques
Influenza activates the immune system and produces inflammation throughout the body. Inflammation can affect existing the fatty plaque deposits that develop inside arteries.
If an unstable plaque ruptures, the body may form a clot at that location. If the clot blocks blood flow to part of the heart muscle, a heart attack can occur.
2. The heart may need more oxygen
Fever and infection can increase the heart rate and metabolic demands of the body. The heart may therefore need more oxygen while the illness is simultaneously making it harder to deliver enough oxygen.
This imbalance can be particularly dangerous when coronary arteries are already narrowed.
3. Flu can reduce oxygen levels
Severe influenza can cause pneumonia and other lung complications. When the lungs cannot transfer enough oxygen into the bloodstream, blood oxygen levels can fall.
The heart still needs oxygen to function normally. Reduced oxygen availability combined with increased cardiovascular demand can put considerable strain on the heart.
4. Infection can affect blood clotting
As said before, acute infections can temporarily alter the body's inflammatory and clotting systems. These changes may contribute to the formation of blood clots, which can potentially block blood vessels supplying the heart or brain.
Studies have shown several overlapping mechanisms; including inflammation, increased metabolic demand, reduced oxygen, changes in clotting, and stress-related hormonal responses, that may help explain the connection between influenza and cardiovascular diseases via the cytokine storm.
How Much Does Flu Increase the Heart Attack Risk?
The increase in heart risk during the flu is not merely theoretical. Many studies have shown higher heart risks in patients of influenza
The CDC confirms that the risk of having a heart attack was about six times higher during the week following an influenza infection. The association was particularly pronounced among older adults and people experiencing their first heart attack.
Another large study examined more than 80,000 adults hospitalized with influenza across eight flu seasons. Approximately 12% experienced an acute cardiac event, including conditions such as acute heart failure or ischemic heart disease.
These figures should not be interpreted as meaning that every person with flu has a 12% chance of having a heart problem.
The study involved people sick enough to require hospitalization, who generally had more severe illness and higher underlying health risks. Still, the findings demonstrate why influenza deserves more attention among people with cardiovascular disease.
Who Is Most Vulnerable?
The risk is especially important for people who already have cardiovascular disease. In fact, heart disease is one of the most common underlying conditions among adults hospitalized with influenza.
People who may need to be particularly cautious include those with:
- Coronary artery disease
- Previous heart attack
- Heart failure
- High blood pressure
- Abnormal heart rhythms
- Heart valve disease
- Other cardiovascular conditions
- A previous stroke
As said earlier, older adults are also more likely to experience serious complications from both influenza and cardiovascular disease. However, a person does not necessarily need to be a heart disease patient to have heart disease risk at flu. Plaque can develop gradually and may remain undiagnosed for years.
How Can the Flu Cause Heart Failure?
Heart failure means the heart cannot pump enough blood to meet the body's needs. An infection such as influenza can increase the body's demand for circulation in the search of more oxygen while also causing fever, inflammation and sometimes pneumonia.
For someone whose heart function is already reduced, this additional burden can trigger worsening symptoms or hospitalization.
People with heart failure should therefore pay particular attention to changes in breathing, swelling, unusual fatigue, or other symptoms during a flu infection and contact their healthcare professional promptly if their condition changes.
In rare cases, influenza can also be associated with direct inflammation of the heart muscle, known as myocarditis, even when the virus haven't directly affected the heart muscle.
How Does Flu Cause a Brain Stroke?
Influenza has also been associated with an increased risk of brain stroke. The mechanisms are likely similar to those involved in cardiovascular complications more broadly. Blood clotting, blood vessel dysfunction and physiological stress during infection may contribute to brain stroke by the blockage of blood flow.
This does not mean that influenza directly causes every stroke. Instead, the infection may act as a trigger in someone who already has underlying susceptibility. That distinction is important because cardiovascular disease develops through multiple factors, including high blood pressure, smoking, diabetes, high cholesterol, age and other conditions.
Does the Flu Vaccine Protect the Heart?
Flu vaccination primarily protects against influenza and its complications. But study also suggests that vaccination may provide cardiovascular benefits, particularly in people at high cardiovascular risk.
A research study on over 9,000 adults found that vaccination reduced major cardiovascular events from about 5.4% to 3.6%, reflecting a relative risk reduction of roughly one‑third. Among people who had recently experienced acute coronary syndrome, the reduction was about 45%.
These findings do not mean that a flu vaccine is a substitute for cholesterol treatment, blood-pressure control, exercise, a healthy diet, or other heart-protective measures.
Instead, vaccination can be considered one additional layer of protection, particularly for people who are vulnerable to both influenza and cardiovascular complications.
What Should People With Heart Disease Do During Flu Season?
If you have heart disease or a previous stroke, prevention becomes especially important.
Get your seasonal flu vaccine
An annual vaccination against influenza for people with heart disease is necessary because they are at higher risk of serious flu complications. Flu vaccines have an established safety record in people with cardiovascular disease.
People with heart disease or a history of stroke should generally not receive the live attenuated nasal-spray flu vaccine; they should discuss the appropriate vaccine option with their healthcare professional.
Continue your regular medications
Do not stop heart or blood-pressure medications simply because you become sick unless your healthcare professional tells you to do so.
It is also sensible to make sure you have an adequate supply of your regular medications before flu season.
Contact your healthcare professional early
If you have cardiovascular disease and develop flu symptoms, contact your healthcare provider promptly. Early antiviral treatment for people with heart disease or a history of stroke who have confirmed or suspected influenza is recommended.
Antiviral medicines work best when started early, so waiting several days before seeking advice may reduce the potential benefit.
Know the warning signs
Flu symptoms can sometimes overlap with symptoms caused by cardiovascular problems. Seek urgent medical attention for warning signs such as:
- Chest pain, pressure or tightness
- Severe or worsening shortness of breath
- Fainting or severe weakness
- New or severe palpitations
- Sudden confusion
- Sudden weakness or numbness, particularly on one side
- Difficulty speaking
- Severe or rapidly worsening symptoms
These symptoms should not simply be assumed to be "part of the flu."
Final Takeaways
The flu is not simply a respiratory illness when it comes to cardiovascular health. Influenza can place substantial stress on the heart and blood vessels, particularly in people with existing heart disease.
The good news is that some of the risks are preventable. Begin Health Life recommends Annual flu vaccination, appropriate treatment when infection occurs, continued management of heart disease, and attention to warning symptoms to help reduce the potential consequences.
For people with heart disease, preventing influenza is therefore not only about avoiding several days of fever and fatigue. It can also be an important part of protecting the heart.