Here is an interesting essay. An excerpt:
That compassion is natural to human beings there is no question. But does it pertain to our higher or to our lower natures? As even or precisely those who take compassion for a virtue acknowledge, it is an emotion. Can an emotion be a virtue? Yes, if the keynote of virtue is naturalness in the sense of spontaneity or authenticity. No, if what defines virtue is the perfection of our nature through the triumph of reason over passion. For this reason the long history of thought about compassion (stretching back at least 2,500 years now) has revolved around just this issue.