In my finishing off the subject of P'ru Ur'vu at

limudtorah.jewishweb.org

The Minchas Chinuch suggested, that according to the Rambam that holds that having pleasure from a Mitzva is considered as having Kavana for a Mitzva, like eating Matzo, so too by P'ru Ur'vu that the Hanah of the Biya makes a Kavan for the Mitzva of P'ru ur'vu

But IMHO (L'Aniyas Dati) I would suggest that there are actually two seperate actions, though they're happening at the same time. The Biya itself is not the mitzva. If you do Biya without letting out seed. you're not doing the Mitzva. So really letting out the seed is the Mitzva, which ther is no particular Hanah involved with that action. So you will still need to manually have Kavanah for it.

This is not compared to eating Matzothat the actual Mitzva is eating, which is the same action that you have pleasure from

Rav chaim,
Would the use of a condom nullify the mitzvah?
Avi

Of course it would (besides the problem of Moitzie Zera L'vatala Shailos.) if she can't get pregnant so how can you do P'ru Ur'vu.

limudtorah.jewishweb.org

http://globalyeshiva.com/eve/forums?a=frm&f=9291076782