Most people think of heart attacks and strokes as problems caused by unhealthy living. Smoking, poor diet, lack of exercise, high blood pressure and high cholesterol are familiar risk factors. But there is another danger that receives much less attention. Common viral infections, including influenza and COVID-19, may substantially increase the risk of heart attacks and strokes, even after the worst symptoms have disappeared. A major scientific review published in 2025 suggests that the connection between infections and cardiovascular disease is considerably stronger than many people realise.
The research, published in the Journal of the American Heart Association, examined 155 studies investigating the relationship between viral infections and cardiovascular disease. The findings were striking. People who contracted influenza experienced approximately four times the usual risk of a heart attack and five times the risk of a stroke during the following month. COVID-19 was associated with roughly three times the usual risk of both conditions over a somewhat longer period. These figures refer to increases in relative risk, not the likelihood that an infected person will actually suffer a heart attack or stroke. For a healthy individual whose ordinary risk is very low, the absolute danger may remain small. Nevertheless, for older people and those with existing heart problems, the increased risk could be significant.
The danger appears to be greatest shortly after infection. In the case of influenza, the first week seems particularly important. Someone recovering from a severe bout of flu might understandably believe that the danger has passed once the fever, coughing and exhaustion have subsided. However, the body's response to the infection may continue to affect the heart and blood vessels. Researchers have found that some of these effects can persist for weeks, while certain studies of COVID-19 suggest that increased cardiovascular risks may continue for considerably longer.
Why should a respiratory infection affect the heart? The answer lies partly in the body's immune response. When a virus enters the body, the immune system launches an attack to eliminate it. This is normally a protective response, but it can also produce inflammation throughout the body. Inflammation affects the walls of blood vessels and can make the blood more likely to clot. For someone who already has fatty deposits in the arteries, this additional strain may be enough to trigger a serious medical emergency.
A heart attack commonly occurs when a blood clot blocks an artery supplying the heart. A stroke can occur when a clot blocks the blood supply to part of the brain. Viral infections may increase the likelihood of these events by making existing deposits in the arteries less stable and encouraging clot formation. In other words, the infection does not necessarily create heart disease from nothing. It may trigger a crisis in someone whose cardiovascular system is already vulnerable. This helps explain why an illness that appears to involve the lungs, throat or nose can sometimes have consequences elsewhere in the body.
The research also points towards risks associated with viruses that remain in the body for long periods. HIV, hepatitis C and the virus responsible for shingles have all been linked to increased rates of cardiovascular disease. Shingles is particularly relevant to older people because it results from the reactivation of the chickenpox virus, which can remain dormant in the body for decades. When the virus becomes active again, the resulting inflammation may temporarily increase the risk of a stroke. The increase is generally much smaller than that observed immediately after influenza, but it is another indication that infections can have effects extending beyond their most obvious symptoms.
Some viruses can also attack the heart muscle directly. This condition, known as myocarditis, involves inflammation of the heart itself. Most people who develop viral myocarditis recover, but a minority experience lasting damage. In severe cases, the heart becomes weakened and less able to pump blood effectively, potentially leading to heart failure. Although myocarditis received considerable publicity during the COVID-19 pandemic, doctors have recognised for many years that a range of ordinary viruses can cause the condition. It is not a problem unique to coronavirus infections.
Another important question concerns repeated infections. Most people experience numerous respiratory infections throughout their lives. If each infection temporarily increases the risk of cardiovascular trouble, could repeated illnesses contribute to the gradual development or worsening of heart disease? This is a reasonable possibility, although researchers have not yet established precisely how much repeated viral exposure contributes to a person's lifetime risk. It would be premature to conclude that every infection causes permanent heart damage. Nevertheless, repeated periods of inflammation and increased blood clotting may be particularly undesirable for people who already have cardiovascular problems.
The findings also raise questions about how heart disease should be prevented. Medical advice traditionally concentrates on exercise, diet, cholesterol, blood pressure and avoiding smoking. These remain essential. However, preventing serious infections may provide another layer of protection. Treatments that control or eliminate certain persistent viruses may also reduce cardiovascular complications.
None of this means that people should become frightened of every cold or minor infection. The research concerns associations between particular viral infections and cardiovascular events, and an increase in relative risk does not mean that a heart attack or stroke is likely to occur. The greatest concern is for people who are already vulnerable because of age, existing heart disease, diabetes, high blood pressure or other medical conditions. For them, a serious infection may represent an additional strain at a time when their cardiovascular system is already under pressure.
There is also a practical lesson about recovery. People sometimes attempt to return immediately to strenuous exercise or demanding physical work after influenza or another significant viral illness. While ordinary activity can generally resume as recovery progresses, persistent chest pain, unusual breathlessness, palpitations or unexplained exhaustion should not simply be dismissed as the lingering effects of a virus. Such symptoms may warrant medical assessment. Sudden chest pain suggestive of a heart attack or signs of stroke require emergency attention, regardless of whether an infection has recently occurred.
The broader message from this research is that infections should not always be regarded as isolated illnesses that begin with a fever and end when the symptoms disappear. They can place additional strain on the heart and circulation, sometimes with consequences that emerge after the original illness seems to have resolved. The human body is an interconnected system, and a virus affecting one part of it can produce effects elsewhere.
For older Australians in particular, this research provides another reason to take serious respiratory infections seriously. Maintaining cardiovascular health remains a matter of sensible diet, regular exercise, controlling blood pressure and avoiding smoking. But reducing the likelihood of severe infections, allowing adequate recovery and paying attention to unusual symptoms may also help protect the heart. The important discovery is not that viruses have suddenly become more dangerous, but that medical science is beginning to appreciate more fully the cardiovascular damage they have long been capable of causing.
https://pmc.ncbi.nlm.nih.gov/articles/PMC10031808/
https://pmc.ncbi.nlm.nih.gov/articles/PMC4834180/