This study is a prospective, observational, two arm parallel group, clinical study involving patients with measurements of Lp(a) and mild to moderate aortic stenosis. A total of 1381 patients underwent measurement of Lp(a) and had a diagnosis of mild to moderate, degenerative aortic stenosis between 2001 and 2020 in Asan Medical Center. Investigators selected a propensity-matched cohort of patients with Lp(a) \>70 mg/dL and those with Lp(a) \<30 mg/dL from the registry of patients with mild to moderate aortic stenosis to control risk factors for progression of aortic stenosis, and try to prospectively compare progression of aortic stenosis between the two groups (Lp(a) \>70 mg/dL versus Lp(a) \< 30 mg/dL). Investigators also evaluate interactions between Lp(a) groups and baseline clinical and echocardiographic variables for progression of aortic stenosis.