Can i stay in US if my H1B extension aproved even my visa expires.

I am currently in US and my H1B extension is aproved . But have not recieved the I797 papers physically still.

Current visa expires on April 13 2014 . Is it valid for me to stay in US beyond this data as my H1B extension is aproved ?

It is ok to stay and work in US on the basis of valid petition and valid I-94 even after the visa stamp in the passport has expired.

The visa stamp is required only when one wants to enter US.