  We investigated the non centrosymmetric superconductors CePt$_3$Si and UIr by
the ac heat capacity measurement under pressures. We determined the pressure
phase diagrams of these compounds. In CePt$_3$Si, the N\'{e}el temperature
$T_{\rm N}$ = 2.2 K decreases with increasing pressure and becomes zero at the
critical pressure $P_{\rm AF}$ $\simeq$ 0.6 GPa. On the other hand, the
superconducting phase exists in a wider pressure region from ambient pressure
to $P_{\rm AF}$ $\simeq$ 1.5 GPa. The phase diagram of CePt$_3$Si is very
unique and has never been reported before for other heavy fermion
superconductors. In UIr, the heat capacity shows an anomaly at the Curie
temperature $T_{\rm C1}$ = 46 K at ambient pressure, and the heat capacity
anomaly shifts to lower temperatures with increasing pressure. The present
pressure dependence of $T_{\rm C1}$ was consistent with the previous studies by
the resistivity and magnetization measurements. Previous ac magnetic
susceptibility and resistivity measurements suggested the existence of three
ferromagnetic phases, FM1-3. $C_{\rm ac}$ shows a bending structure at 1.98,
2.21, and 2.40 GPa .The temperatures where these anomalies are observed are
close to the phase boundary of the FM3 phase.
