Aortic valve stenosis is the most frequent reason for prosthetic valve replacement in adults. Its incidence increases with age. Development of the most frequent form, degenerative-calcific aortic stenosis, is related to atherosclerotic risk factors. The narrowing of the aortic valve orifice leads to creation of a systolic pressure drop, the gradient, between left ventricle and ascending aorta. The pressure overload from aortic stenosis causes concentric left ventricular hypertrophy and later heart failure. Typical symptoms of severe aortic stenosis include dyspnea, angina, and dizziness or syncope. On auscultation, a loud systolic murmur over the base of the heart is apparent, which is transmitted to the carotids. The ECG often shows left ventricular hypertrophy. The most important diagnostic technique is echocardiography, which allows to measure the gradient and to calculate the orifice area, which determine the degree of severity. The development of symptoms or impaired left ventricular function in severe aortic stenosis should prompt surgical treatment by valve replacement. Truly asymptomatic patients with preserved left ventricular function should be followed conservatively.