There is no one definitive answer to this question. It depends on the language you are speaking and the context in which you want to say it. In English, some possible translations of forever in our hearts could be always in our hearts, eternally in our hearts, or for all time in our hearts. It is a phrase that expresses deep love and commitment, so it can be used in many different situations - from telling someone they will always be loved, to writing in a sympathy card for someone who has lost a loved one.