I find myself sceptical about this. And not only because so many claims about COVID-19 have turned out to be false.

We start with the opening claim, "COVID-19 causes cardiac dysfunction in up to 50% of patients". I wonder how they are defining patient and cardiac dysfunction in this sentence, as it is well known that virtually all people who get COVID have an extremely mild infection, and often no symptoms at all. If we look at e.g. the UK report of hospital admissions [1] then we can see that cardiac admissions plunged during the lockdown period and then returned to normal. If COVID was really damaging hearts at such a high rate, that would presumably have been noticed before now in more people being admitted to hospital with heart problems. Instead there was a huge drop.

But perhaps by dysfunction they mean a mild sort of damage that would take a fairly long time to detect. Where did they get this 50% figure from?

The abstract doesn't use citations but the introduction does cite three studies. It says:

"Notably, multiple independent reports have found that COVID-19 patients frequently present with significant myocardial damage6–8, even without prior cardiovascular disease9 (CVD), indicating that viral infection may be directly responsible for the cardiac damage"

Obviously we would expect CVD to be co-present with COVID-19 in many patients because COVID-19 only kills the very old and frail, but they also cite one study as evidence it also shows up in patients who didn't previously have any heart damage. That study is a statistical meta-analysis [2]. This study contains the following curious statement:

"SARS-CoV-2 may invade cells by binding to ACE2, causing direct damage to cardiomyocytes. However, the autopsy results of COVID-19 cases failed to detect SARS CoV-2 virus components in myocardial tissue by electron microscope observation, immunohistochemical staining or PCR"

... which seems to contradict the headline. However this new study works by bathing heart cells derived directly from stem cells with virus in a lab, so it's not really a close equivalent of the real body. Their claims about autopsy specimens also showing SARS-CoV-2 invasion of the heart must be taken with a dose of salt, as:

"The alarming clinical consequences of COVID-19 on the heart have been puzzling since the vast majority of pathological studies of autopsy patients have not shown any specific signature of COVID-19 in cardiomyocytes ... We obtained autopsy specimens from three COVID-19 positive patients, one of whom was diagnosed with viral myocarditis"

So their claim that it's a "heart virus" requires discarding the majority of the evidence from prior studies that it doesn't show up in the heart, and extrapolating from a whole three patients. In fact the meta-analysis they cite in support of their primary alarming claim speculates the the heart damage isn't caused by the virus at all, but rather by general increased stress on it due to breathing difficulties stemming from the respiratory infection, which would make more sense.

The meta-analysis meanwhile is heavily biased towards people who died, and is thus not at all representative of the real population. They admit this:

"The overall mortality rate was 23.5% in our meta-analysis, which is much higher than the value of 2.3% of 44,672 confirmed cases reported in the study of the Chinese Centers for Disease Control and Prevention. A possible reason is that these involved studies included a high proportion of critically ill patients."

So it's really not obvious how these findings generalise to the actual population, where doctors are not reporting huge waves of previously healthy patients turning up with otherwise inexplicable heart damage.

[1] https://assets.publishing.service.gov.uk/government/uploads/...

[2] https://www.ncbi.nlm.nih.gov/pmc/articles/PMC7189258/