Is it ultimately selfish to do good for others?

I am a Christian.   I have heard the arguments that Christians only do good for the sake of getting a reward (Heaven). I don't do good for a reward. 

I have chosen life - in Jesus - and what comes along with choosing life is a conversion of heart mind and soul.  This is me being a new creature; a new creature who lives in the light of the Lord God.  The nature of God is love, kindness, grace (generosity), forgiveness, goodness, patience and many other positive things.  I have no joy unless I'm doing what pleases the Lord.  I don't enjoy worldly things anymore.    As I walk with Jesus throughout my life, I am refined and I take on the nature of Him more and more as I go along.  I willingly want to share Jesus' goodness with others and help others however I'm needed and/or can help.   This is not to "GET" something(Heaven)  - it is because I've a changed nature - changed to match the nature of God.   

If we try to do things to get into heaven (thought of by people as a reward), we will never get there. The ONLY way to heaven is to turn to Jesus and accept the gift of life that he offers.   It is therein that the conversion and longing to do good lies.