Reward in Heaven? What is it? (Catholic)

Catholic Church teaches that we will be rewarded differently in heaven based on our merit (i.e. based on the amount of good deeds that we have freely done during our earthy life; for example, see this article from [International Catholic University](http://icucourses.com/pages/016-12-merit-god-works-with-us)) . My question is, what exactly is this "heavenly reward"? I have heard some saying that the heavenly reward is our heavenly capacity for love (with greater the reward implies having a greater heavenly capacity for love), but I cannot really find a source of this claim. What exactly will our "heavenly reward" be? Please answer according to Catholic understandings.