Compassion

Compassion is the desire to enhance the welfare of someone in need.

It differs from empathy, which is about mirroring and understanding someone else’s emotions. Heroism can be seen as compassion in action under adverse conditions, but it is not evident that compassion is a necessary prerequisite for heroic behavior.

Altruism

Altruism is the unselfish concern for the welfare and well being of others.

It is the active practice of love and compassion. Altruism is demonstrated in daily life by simple acts such as feeding the hungry and providing directions to a stranger in need.  Altruism focuses on a motivation to help others or a want to do good a good thing, without a concern for reciprocation or reward. Altruism is related to heroism; however it lacks an element of risk to the helper. Research indicates that altruism is triggered by empathy and driven by compassion.

References:
Cialdini, Robert B. (1987). Empathy-Based Helping: Is it selflessly or selfishly motivated? Journal of Personality and Social Psychology.
Cialdini, Robert B. (1997). Reinterpreting the Empathy-Altruism Relationship: When One into One Equals Oneness. Journal of Personality and Social Psychology. Vol. 73.
Keltner, D. (2009). Born to be good: The science of a meaningful life. New York, NY: Norton.