Acute myocarditis (AM) in athletes is a frequent source of concern.

Investigate whether the way of practice has an impact on the severity of AM and on the occurrence of long-term adverse events if sport is resumed.

82 athletes (≥2hours of sport per week) who presented an AM were retrospectively included from January 2009 to December 2019. AM was defined by onset of symptoms<1 month and a positive endomyocardial biopsy (Dallas criteria) or a positive CMR (2 or 3 Lake Louise Criteria) associated with an elevation of troponin. The habits of practicing sport before and after AM were collected. Endpoints were severe AM, defined by a left ventricular ejection fraction<50% or the use of inotropic drugs or ventricular assist device, and the occurrence of late (>6 months after acute phase) heart failure, rehospitalization or recurrence.

Mean age was 29±9 years old, 77 (94%) were men, median time of practice was 5.4±3.7hours per week. Sixteen (29.5%) presented a severe AM. Practicing sport>6hours a week (43.8% vs. 16.7% P=0.019) or a Mitchell's Class IIIA sport (37.5% vs. 10.6%; P=0.008) was associated with severe AM. Practicing a Michell's Class IC sport (6.3% vs. 37.9%; P=0.008) was associated with non-severe AM. Median follow-up was 33.8 [16.6–60], 65 (79.3%) patients resumed sport (Fig. 1). In univariate Cox regression analysis, sport resumes (HR 0.97; 95% CI 0.20–4.57, P=0.97), competition (HR 0.76; 95%CI 0.15–3.82; P=0.74) and amount of hours of practice par week (HR 1.15; 95%CI 0.98–1.32; P=0.06) were not associated with the occurrence of late heart failure, rehospitalization or recurrence (Table 1).

In athlete's AM, the way of sport participation (static or dynamic component, practice over 6hours a week) is associated with the presentation's severity. The return to sport after the acute phase does not seem to be associated with the occurrence of adverse events.