The mitral valve is an important part of the left heart system, located between the left ventricle and the left atrium. When the heart is in diastole, the mitral valve opens, allowing blood from the atrium to be transferred into the ventricle. However, when the mitral valve is narrowed, blood from the left atrium cannot flow into the left ventricle in a timely manner. This leads to an increased load on the left atrium. Over time, this can cause severe enlargement of the left atrium and lead to atrial fibrillation, a type of cardiac arrhythmia. Once atrial fibrillation occurs, it can cause thrombosis in the left atrium, particularly in the part called the atrial appendage. If a thrombus forms, it may dislodge during the heart's contractions, potentially causing systemic embolism with serious consequences, including paralysis or even sudden death.