Rheumatic heart disease often occurs in the southern regions where there is a higher level of humidity. Some patients develop rheumatic heart disease after suffering from rheumatic arthritis or other rheumatic conditions. In Western medicine, it is believed to be due to a series of immune system damages caused by infection with Group A streptococcus, leading to rheumatic inflammation of the heart or damage to the valve functions. This often presents as mitral stenosis, atrial fibrillation, or pericardial effusion. Therefore, according to traditional Chinese medicine theory, rheumatic heart disease is related to humidity.