The NEJM details a case of myocarditis
This is what I believe Red Sox manager Terry Francona has. Some lasting effects from this disease:

Whereas most patients with acute viral myocarditis recover spontaneously, a dilated cardiomyopathy develops in approximately one in five patients. As for all patients with systolic dysfunction, treatment primarily includes angiotensin-converting”“enzyme inhibition and beta-blockade. Given the role of autoimmunity in myocarditis-induced damage, immunosuppressive therapy has also been used. However, randomized studies of azathioprine and cyclosporine have not shown benefits. Although this patient’s follow-up echocardiogram showed some early signs of improved wall motion, a substantial minority of patients never regain normal cardiac function.