Beat the softened cream cheese in a large bowl until completely smooth and free of lumps.
Add the powdered sugar to the cream cheese and continue mixing until fully incorporated.
Pour the fresh lemon juice and zest into the mixture while blending on low speed.
Whip the heavy cream in a separate bowl until stiff peaks form.
Fold the whipped cream gently into the lemon mixture using a rubber spatula.
Spoon the lemon cheesecake mixture evenly into the graham cracker tart shells.
Smooth the surfaces using a small offset spatula.
Place the tarts on a flat tray and refrigerate for at least 4 hours until firm.