The most common sign of stenosis is an apical diastolic low-pitched rumbling murmur, which is characterized by a low-pitched, limited, incrementally increasing murmur that can be heard in the apical diastolic phase, mainly in mid- to late-diastole, and reaches its highest pitch before the systolic phase. The murmur can be heard in the left lateral recumbent position when the patient has an increased murmur and can be indistinguishable when the heart rate is faster or when atrial fibrillation is present. The mechanism of this symptom is mainly due to the pressure step difference between the valve orifices caused by mitral stenosis. In mild to moderate mitral stenosis, there is a positive correlation between murmur loudness and increasing pressure gradient, i.e., the more severe the stenosis, the higher and more pronounced the murmur sound. However, in advanced cases, when the stenosis is severe, the murmur is not audible.