A Credit Card is an item debuting in the first Kid Icarus game. This handy item, only obtainable in Treasure Chambers by outsmarting the God of Poverty, allows Pit to purchase items from a Black Marketeer. It works slightly different in the two games it appears in.
If Pit has this in his inventory while not having enough Hearts to purchase an item from the Black Marketeer, and he collects the item, his Heart total will be reduced to 0 and the rest will be placed as debit on the card. Until he collects enough Hearts to equal out the balance, nothing more will be added to his total and Pit will be unable to buy anything else until the debt is paid off.
Like in Kid Icarus, Pit can only find a Credit Card by outsmarting the God of Poverty, who will reward Pit with a random item. Only one Credit Card can be collected at any given time. If Pit enters a Black Market and attempts to buy something with the Credit Card in his inventory, he will trade the Credit Card for the item. Unlike in Kid Icarus, Pit's Hearts are not reduced, but the Credit Card is used even if Pit has enough Hearts to buy the item.