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Visiting Iran does NOT invalidate an existing US visa.
People that have visited Iran recently are not able to enter the US using the Visa Waiver Program, which is why an existing ESTA will be invalidated when visiting Iran.
However this is not the case for someone entering the US using a visa, so your visa is still valid after such a visit.
As is always the case, when entering the US you can be questioned and potentially refused entry to the country. It is very possible you will be questioned about your trip to Iran, but presuming it was for tourist or similar purposes then I would not expect you to have any issues, and countless people have done this before you without issue.