How is a diagnosis made? Women get blood clots all of the time. It's a common complication of hormonal birth control. Thus they're more likely to understand the symptoms and have it treated before it becomes a problem, and what might get diagnosed as myocarditis instead gets coded as birth control related blood clots. And that's if they're doing anything stenuous to trigger a heart attack.

To phrase it differently, the situation is worse than it looks and we need more data.