The magician produces a stack of business cards. On the back of one business card is a drawing of a deflated balloon. A spectator signs his/her initials in the corner of the card. That card is placed aside, temporarily out of sight but not out of mind. A card is then selected, memorised and lost back in the deck. For example, the card happened to be the 4 Clubs. The magician then takes the business card that was set aside and blows on it (as if to blow a balloon). The drawing of the deflated balloon is now all 'blown up', with the '4C' displayed in the middle of the balloon. The business card is handed out as a souvenir.
This effect makes use of the 'Out to Lunch' principle and the 'master move', which can be found on pg 165 - 166 of 'Mark Wilson's Complete Course in Magic' by Mark Wilson.
