  This work deals with the influence of the gravitational field produced by a
charged and rotating black hole (Kerr-Newman spacetime) on massive scalar
fields. We obtain an exact solution of the Klein-Gordon equation in this
spacetime, which is given in terms of the confluent Heun functions. In the
particular case corresponding to an extreme Kerr-Newman black hole the solution
is given by the double confluent Heun functions. We also investigate the
solutions in regions near the event horizon and far from the black hole.
