The most common manifestation of rheumatic heart disease involves the mitral valve, leading to severe stenosis and insufficiency of the mitral valve, and decreasing the amount of blood returning to the heart. At this time, there is not enough blood returning to the heart, and naturally, the amount of blood pumped out is reduced. If it is extremely severe, it can lead to fainting; this is the first scenario.

The second scenario is rheumatic heart disease affecting the aortic valve, which can also result in insufficient blood being pumped out, causing ischemia and hypoxia in the cerebral arteries, leading to fainting.

Another situation is related to heart arrhythmias, which are divided into two types. One type occurs when rheumatic heart disease is very severe, potentially causing atrial fibrillation. Some patients with cardiac bypass might experience ventricular fibrillation, leading to fainting. Additionally, there is a scenario where severe rheumatic inflammation causes dysfunction in the heart's conduction system, leading to conditions similar to sick sinus syndrome or complete atrioventricular block, causing significantly slow heart rhythms, which may also lead to fainting.