ACE2 and aortic stenosis: The aims of our study were to investigate (1) ACE2 dysregulation in AS patients, and correlation of serum ACE2 activity to disease severity, kidney function, and overall inflammatory state; (2) the effect of Renin-Angiotensin-Aldosterone system (RAAS) inhibitors on ACE2 activity; and (3) the effect of aging on serum ACE2 activity.