Pig and cow valves will calcify and fail eventually. But it’s a slow process so you have time to plan and make decisions for replacement. Mechanical values are great until one day the clicking sound stops and you need to get to a hospital ASAP.

Back in the 90’s there were a series of values where the flipping plate shattered-sending shrapnel into the heart and beyond. Typical failure mode is stuck open which is survivable. Stuck closed is very bad.