Rheumatic heart disease refers to changes in the heart and heart valves caused by a disruption in the body's immune system following infection by Group A Streptococcus. Some also exhibit signs of heart inflammation and pericardial effusion, commonly presenting mitral stenosis, aortic valve stenosis or insufficiency, and tricuspid valve insufficiency. Myocarditis, on the other hand, refers to direct invasion of the heart muscle by viruses or bacteria, leading to heart muscle damage and cardiac dysfunction. Some cases present with arrhythmias, while others exhibit heart failure or shock, which can be severe enough to cause death. Generally, rheumatic heart disease has a longer course of illness, whereas myocarditis tends to improve within about two weeks. However, fulminant myocarditis has a high mortality rate, often accompanied by symptoms of heart failure, and some patients may suffer from long-term arrhythmias as a complication.