Have Visa but didnot visit U.S,will it get cancelled

[Binal]

My father has got 10yr tourist visa few of months back. But due to some reason he couldn't accompany my mother to visit U.S

After the visa is issued does he have to visit U.S within some time period. If he cannot visit U.S for 1-2yrs after the visa was issued, will his visa get cancelled or revoked?
Does he have to visit U.S within certain period?

Any help on this is appreciated.

Thanks,
Binal

[yuvayuva]

The visa remains valid. He can travel anytime he wants.