It's two different words for two different places based on the different descriptions of two different religions. Heaven is described in the Christian bible as being a place that God is filled with, and only God's divine creatures (like angels) and people who believed in Jesus Christ as their savior are allowed to live in. Paradise is the Islamic belief in the afterlife, and they have a different description, and their ideas of who may enter is not based on Jesus, but on their belief in, worship and sacrifices to their god, Allah.

From what I hear, heaven is for good Christians only and Paradise is the end of the line for good Muslims. Both places have a lot of virgins, but in Paradise, the virgins are just waiting there to service all the martyrs that make the grade. In heaven, the virgins are apparently doomed to remain so for eternity.