Over time, they also close against each other with very little wear and tear, which explains how this mechanism continues to work seamlessly for more than 2 billion beats a heart gives in its lifetime.
Purjeet sulkeutuvat toisiaan vasten eivätkä hioudu tai kulu ja sen takia sydän  toimii juoheasti, ja sykkii elinaikana yli kaksi miljardia kertaa.