In this study we compare different methods (biopsy, MRi, CT, echocardiography and different biomarkers) to evaluate the extent of MF in 130 patients with severe aortic stenosis undergoing AVR. We will focus on their symptom improvement and survival rate one year after the operation. Our main thesis is that patients with severe fibrosis before the operation have little or no symptom improvement and reduced survival after the operation. If this thesis is correct, it will question which patients to offer AVR. Some patients we operate today may have no benefit from the operation because the left ventricle is damaged from severe fibrosis, and some patients from who we withhold the operation today because they are asymptomatic may benefit from AVR before they develop severe fibrosis.