Aortic valve stenosis (AS) affects 2-7% of persons \> 65 years, symptoms include: angina and dyspnea, dizziness and syncope. Coincidence of coronary artery disease (CAD), also presenting with angina and dyspnea, in patients with AS between 40 - 65% . Angina in AS caused by significant reduction of coronary flow reserve (CFR). CFR is the ratio of maximal flow increase in the coronary vessel bed during maximal hyperaemia (medically or exercise induced). FFR (fractional flow reserve) use in patients with AS potentially invalid due to dysfunctional CFR leading to potential undertreatment of CAD in these patients.CFR disturbance in AS mainly due to myocardial overload causing concentric hypertrophy, increased oxygen consumption and neurohormonal activation leading to increased vascular resistance. Current studies are investigating the validity of FFR and iFR in AS patients. Recent data demonstrate very good correlation between FFR and iFR derived values to PET myocardial perfusion imaging values in patients with no evidence of AS. Our study aims to investigate the diagnostic performance of FFR and iFR in intermediate-grade coronary stenosis in patients with severe aortic valve disease and correlate FFR- and iFR derived values with those extracted from PET-perfusion Imaging.