When the aortic valve narrows and becomes stenotic a pressure gradient develops between the left ventricle of the heart and the aorta. In individuals with AS the left ventricle has to generate an increased pressure in order to overcome the increased afterload resulting from the stenotic aortic valve and eject blood out of the LV. As a result of the increased pressure that the left ventricle has to generate, the myocardium of the LV eventually undergoes hypertrophy, observed as a thickening of the left ventricles walls, and as a result the action of the heart is weakened (heart failure). Surgery to replace the aortic valve should generally be arranged to take place before ventricular hypertrophy begins to develop, as the damage may be irreversible.
When the condition is symptomatic, patients usually describe symptoms of anginal chest pain, breathlessness or syncope. Chest pain arises either as a result of co-existing coronary artery disease (present in up to 30% of those with AS) or due to the 'mismatch between the oxygen supply and demand of the hypertrophied left ventricle working against the high pressure outflow tract obstruction.