Which finding is most characteristic of rheumatic mitral stenosis?

The finding most characteristic of rheumatic mitral stenosis is the presence of a rumbling diastolic murmur. This murmur occurs due to the turbulent blood flow across the narrowed mitral valve during diastole. In the case of rheumatic mitral stenosis, the valve becomes stenosed or narrowed, often resulting from rheumatic fever, and this particular sound is indicative of the obstruction to blood flow that occurs when the left atrium empties into the left ventricle.

The murmur typically has a low-pitched "rumbling" quality and is best heard with the patient in the left lateral decubitus position, utilizing the bell of the stethoscope. This characteristic sound reflects the hemodynamic changes associated with the turbulent blood flow through the mitral valve during diastole, highlighting the severity of the stenosis and the effects it has on cardiac function.