Now, it is time to define myocarditis. This is a rather rare disease. The primary cause is a viral infection. Another reason for the disease to show up is the opposite reaction of an immune system. When this defender of organism starts attacking individual’s body instead of fighting external threats, a strange reaction appears: it’s like one friend attacking his best friend. This phenomenon is often noticed during lupus attacks, so it is important to know the difference between myocarditis and similar cases.