Avoir le cœur sur la main is a wonderful French expression that literally means “to have the heart on the hand” and translates to “to have a heart of gold” or to be big, open and kind-hearted. A French-to-French translation is être généreux (to be generous).
Avoir le cœur sur la main
To have a heart of gold, to be big-hearted

Example setence
Paul est tellement généreux. Il invite ses amis chaque été pour faire un barbeque au bord du lac. Il adore inviter les enfants à faire du ski nautique. Il a vraiment le cœur sur la main.
Paul is so generous. He invites his friends every summer to have a barbeque on the lake. He loves to invite the kids to go water skiing. He really has a heart of gold.