**3.8 Epidemiology and aetiology**

Isolated aortic stenosis (AS) is more frequent in men and is found in 2% of people 65 years of age and older. The most frequent causes of AS include agerelated calcific degeneration, bicuspid aortic valve, and rheumatic aortic valve. The distribution of these causes diverges across age groups and geographic regions. Age-related degeneration is the commonest cause of AS in elderly patients. In comparison, bicuspid aortic valve calcification accounts for most surgical cases in younger patients (>65) [33].
