Magento

I added some new attributes in my list of attributes in Catalog/attributes/manage the attributes
and j’ would like now to use them everywhere in my site. These attributes post automatically on the catalog/product
but I want to use in the checkout/cart.
I used this code
<?php echo $_product->getData('ref'); exit; ?> ==>nothing
what I must declare them in code or what to make ????
Help me plz :-(