Pulmonary capillary pressures in this level cause an imbalance between the hydrostatic pressure and the oncotic pressure, leading to extravasation of fluid from the vascular tree and pooling of fluid in the lungs (congestive heart failure causing pulmonary edema).The constant pressure overload of the left atrium will cause the left atrium to increase in size. As the left atrium increases in size, it becomes more prone to develop atrial fibrillation (AF). When atrial fibrillation develops, the atrial kick is lost (since it is due to the normal atrial contraction).In individuals with severe mitral stenosis, the left ventricular filling is dependent on the atrial kick. The loss of the atrial kick due to atrial fibrillation ( i.e. blood cannot flow into the left ventricle thus accumulating in the left atrium )  can cause a precipitous decrease in cardiac output and sudden congestive heart failure.Patients with mitral stenosis prompts a series of hemodynamic changes that frequently cause deterioration of the patients clinical status. A reduction in cardiac output, associated with acceleration of heart rate and shortening of the diastolic time, frequently leads to congestive heart failure. In addition, when AF sets in, systemic embolization becomes a real danger.Mitral stenosis typically progresses slowly (over decades) from the initial signs of mitral stenosis to NYHA functional class II symptoms to the development of atrial fibrillation to the development of NYHA functional class III or IV symptoms. Once an individual develops NYHA class III or IV symptoms, the progression of the disease accelerates and the patients condition deteriorates.
Mitral stenosis is a valvular heart disease characterized by the narrowing of the opening of the mitral valve of the heart. It is almost always caused by rheumatic valvular heart disease. Normally, the mitral valve is about 5 cm2 during diastole. Any decrease in area below 2 cm2 causes mitral stenosis. Early diagnosis of mitral stenosis in pregnancy is very important as the heart cannot tolerate increased cardiac output demand as in the case of exercise and pregnancy. Atrial fibrillation is a common complication of resulting left atrial enlargement, which can lead to systemic thromboembolic complications like stroke. Signs and symptoms
Signs and symptoms of mitral stenosis include the following:

Heart failure symptoms, such as dyspnea on exertion, orthopnea and paroxysmal nocturnal dyspnea (PND)
Palpitations
Chest pain
Hemoptysis
Thromboembolism in later stages when the left atrial volume is increased (i.e., dilation). The latter leads to increase risk of atrial fibrillation, which increases the risk of blood stasis (motionless). This increases the risk of coagulation. Ascites and edema and hepatomegaly (if right-side heart failure develops)Fatigue and weakness increase with exercise and pregnancy. Natural history
The natural history of mitral stenosis secondary to rheumatic fever (the most common cause) is an asymptomatic latent phase following the initial episode of rheumatic fever. This latent period lasts an average of 16.3 ± 5.2 years.