  The properties of the novel heavy fermion superconductor Ce$_3$PtIn$_{11}$
are investigated by thermodynamic and transport measurements at ambient and
under hydrostatic pressure. At ambient pressure the compound exhibits two
successive magnetic transitions at $T_1$ $\approx$ 2.2 K and $T_{\rm N}$
$\approx$ 2 K into antiferromagnetically ordered states and enters into a heavy
fermion superconducting phase below $T_{\rm c}$ $\approx$ 0.32 K. The
coexistence of long-range magnetic order and superconductivity is discussed in
the context of the existence of the two crystallographically inequivalent
Ce-sites in the unit cell of Ce$_3$PtIn$_{11}$. The experimental data allow us
to construct the pressure-temperature phase diagram.
