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In page Artificial heart valve:
"Introduced in 1969, the first clinically available tilting-disc valve was the Bjork-Shiley valve.[1] Tilting‑disc valves, a type of swing check valve, are made of a metal ring covered by an ePTFE fabric. The metal ring holds, by means of two metal supports, a disc that opens when the heart beats to let blood flow through, then closes again to prevent blood flowing backwards. The disc is usually made of an extremely hard carbon material (pyrolytic carbon), enabling the valve to function for years without wearing out.[citation needed]
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