Blood is difficult to pass from the left atrium to the left ventricle due to narrowing of the mitral valve. The amount of blood that accumulates in the left atrium can causes it to swell up. These causes irregular heartbeats (palpitations) – Atrial fibrillation. The blood further backlogs into the lungs where it can cause raised blood pressure in the lungs (pulmonary hypertension), water accumulation and breathlessness.

Mitral stenosis is most often caused by Rheumatic Fever which may have been caught and recovered from many years beforehand. Rheumatic Fever is an inflammatory disease that occurs in a small number of patients after throat infections caused by a bacteria called streptococcus pyogenes. Now that understanding of and treatments for this are better understood, it is rare to develop Rheumatic Fever in Singapore.