On histological examination the inflammation may be focal or diffuse [3]. The presence of dead or degenerated cardiac myocytes with surrounding inflammation is the hallmark of the disease process.
Macroscopically, the heart may develop biventricular dilation but the valves and subendocardium are normal. Fibrosis of the damaged tissue over time results in poor cardiac contractility and function and may result in conduction abnormalities. Myocarditis may progress to a dilated cardiomyopathy in some cases, particularly those of a viral aetiology.
Many aetiological agents have been implicated as causes of myocarditis. These include a wide variety of infectious agents, systemic diseases, drugs and environmental toxins. Around half of all cases are idiopathic [4].
The following pages discuss these aetiological agents in more detail.

Learning bite

The histological hallmark of myocarditis is dead myocytes with surrounding inflammatory infiltrates.