Magento: Session Success or Failure Message after redirect – Magento HowTo
Add a Success, Info or Error Message to the session and save this for re-direction in Magento
//A Success Message Mage::getSingleton('checkout/session')->addSuccess("Your cart has been updated successfully!"); //A Error Message Mage::getSingleton('checkout/session')->addError("Your cart has been updated successfully!"); //A Info Message (See link below) Mage::getSingleton('checkout/session')->addNotice("This is just a FYI message..."); //These two lines are required to get it to work session_write_close(); //THIS LINE IS VERY IMPORTANT! $this->_redirect('checkout/cart');