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Heart valve development and disease. During embryonic development, endocardial cushions are present in the outflow tract that elongate and stratify into valve leaflets after birth. Valve layers consist of fibrosa (yellow), spongiosa (blue), and atrialis (black). Bottom panels depict myxomatous alterations associated with connective tissue mutations (left) and calcification of aortic valves characteristic of aortic stenosis (right).
