  We investigate the heat current of a strongly interacting quantum dot in the
presence of a voltage bias in the Kondo regime. Using the slave- boson
mean-field theory, we discuss the behavior of the energy flow and the Joule
heating. We find that both contributions to the heat current dis- play
interesting symmetry properties under reversal of the applied dc bias. We show
that the symmetries arise from the behavior of the dot trans- mission function.
Importantly, the transmission probability is a function of both energy and
voltage. This allows us to analyze the heat current in the nonlinear regime of
transport. We observe that nonlinearities ap- pear already for voltages smaller
than the Kondo temperature. Finally, we suggest to use the contact and electric
symmetry coefficients as a way to measure pure energy currents.
