Valves are incredibly thin, floppy little affairs, and in general, they do not form perfect seals when they close. And in general, a healthy heart is so adaptable that a little leakage is compensated for. As long as the leakage is described as trivial, mild, or even moderate (if stable), it's not too big an issue.
However, the aortic valve is the exception: that one should not leak or 'regurgitate.' If it does, it needs to be looked at more carefully and monitored as well. Mine leaks. It has for years, but I get regular stress and echo tests, and mine remains stable as 'mild to moderate. I have no symptoms, and the chances are that I will live out my life without problems related to this.
If the valve fails, replacement surgeries of several types are possible.