When a Cold Becomes Dangerous for the Heart: A Cardiologist Explains

With the symptoms mentioned, you should see a general practitioner or, better yet, a cardiologist. An ECG and laboratory tests are important, including measurements of inflammatory markers. The cardiologist will also perform an echocardiography – a cardiac ultrasound – which can already reveal a great deal.

If more severe symptoms occur, however – such as impending loss of consciousness, persistent chest pain, or severe shortness of breath – you must call 112 and request an ambulance immediately.

How can an initially harmless infection develop into myocarditis?

We should not alarm people unnecessarily. A slight runny nose does not mean someone will develop myocarditis the next day.

There is a saying: "Three days coming, three days staying, three days going." But if an infection lasts longer than usual – for example, one or two weeks – viruses can pass through the inner lining of blood vessels and reach other organs.

There are other mechanisms at work as well. With more complex viruses in particular, an immune response can develop that turns against the body's own structures – a process known as a cross-reaction.

To put it simply: viruses are foreign bodies. To defend itself, the immune system produces antibodies. Sometimes these antibodies cannot adequately distinguish between foreign proteins and the body's own proteins, so they also attack the body's own cells – such as heart muscle cells. This results in an autoimmune reaction.

These processes do not develop overnight, which is why involvement of the heart muscle can also occur with a time delay.

Why Exercise During a Cold Can Be Dangerous

When is it safe to exercise again after a cold?

Only once the symptoms have largely subsided. Even coughing, hoarseness, or a runny nose should be reason enough to avoid exercise. That doesn't necessarily mean you have to stay in bed – you can still work at your desk. But the gym, jogging, or cycling should all be avoided during a cold or flu. It is better to take it easy, stay home more, and get to bed earlier.

I see a real need for public education here, and I say that from painful clinical experience. I have treated younger patients who were very sporty and driven, and who kept training while they had a flu-like illness because they believed they could somehow push through the infection. That is simply not possible.

There are also scientifically sound guidelines from the European Society of Cardiology, the ESC, on this very subject. What matters most is monitoring how the illness progresses. In autumn especially, I regularly see patients who come to my practice for follow-up checks. If their lab values are still abnormal, or if they are still sweating at night, continuing to cough, hoarse, or feeling unusually run-down, they should wait before returning to exercise.

From my clinical experience, I am also well acquainted with the negative outcomes that result when the necessary rest is not observed. Failing to rest can lead to considerable damage to the heart muscle, and in the worst case, even permanent heart failure.

How long does it take for the heart to recover from myocarditis?

In the past, physical rest of three to six months was the standard recommendation for myocarditis, and it was an approach I followed during my time at the university as well. The more recent ESC guidelines take a more nuanced view, with the focus now on the individual course of the illness. That said, we are still often talking about many weeks to several months.

I am thinking right now of a young teacher who has been coming to see me regularly for several months. Even after three months, his ECG still shows changes known as T-wave inversions.

We also performed a cardiac MRI, which allows us to assess the structure of the heart muscle in great detail. In myocarditis, typical changes appear on the scan, such as edema, and possibly also tissue damage and scarring.

In this patient's case, the MRI findings have fortunately improved significantly. For this reason, we have only gradually increased his physical activity. He is now allowed to go for walks, which I had previously forbidden. Strenuous exercise, however, is still not permitted.

How is myocarditis or pericarditis treated?

The most important thing initially is physical rest. In more severe cases, inpatient treatment may be necessary, while in milder cases the required rest can be maintained at home. Staying well hydrated is also important.

For painful pericarditis, anti-inflammatory medications are an option. I use anti-rheumatic drugs such as diclofenac, among others, and have had very good results with them over many years of practice. Colchicine is also among the medications I use as a cardiologist.

When it comes to invasive procedures, however, I am cautious. In the past, cardiac catheterizations with tissue biopsies were sometimes performed. The new 2025 ESC guidelines also take a nuanced view of such interventions.

For me, the decisive question is always what therapeutic consequences a given examination will actually have. You should not do everything just because it is technically possible.

When Myocarditis Causes Lasting Damage to the Heart

What are the worst possible consequences of myocarditis?

Sudden cardiac death. The most devastating outcome is the development of ventricular tachycardia, a dangerous cardiac arrhythmia that can progress to ventricular fibrillation. Without immediate intervention, this can be fatal within a very short time.

There are other severe outcomes as well. In some patients, the heart muscle is so severely damaged and scarred by the inflammation that dilated cardiomyopathy develops, leaving the heart permanently weakened. Those affected have reduced physical capacity and may experience shortness of breath even when climbing stairs. In the worst cases, the heart failure is so severe that patients are placed on the waiting list for a heart transplant.

Those are, of course, the most devastating outcomes.

What advice would you give to people who are currently going through a cold?

The most important thing is to take a flu-like illness seriously and rest sufficiently. As a preventive cardiologist, I normally encourage people to get as much exercise as possible. During an infection, however, exactly the opposite applies. You should only return to physical activity once the symptoms have largely subsided.

You should also avoid taking antibiotics unnecessarily. Antibiotics do not work against viral infections, and there need to be concrete signs of a bacterial infection before they are warranted. I therefore consider it important to carefully assess whether a bacterial infection is actually present before starting antibiotic therapy.

And if particular symptoms arise – such as chest pain, shortness of breath even with minimal exertion, or cardiac arrhythmias – you should definitely see a doctor.