We study the dynamics of the gas flow discontinuities after pulse ionization of a half space in front of a flat shock wave moving in a channel. Pulse volumetric electric discharge initiated in the vicinity of the shock concentrates in front of the shock and heats the gas there. The heating is shown to be very rapid. We use the shadow imaging technique and a high speed camera to study the flow pattern evolution after the discharge. The pattern consists of two shocks separated by a contact surface. This structure corresponds to the classical Riemann problem formulation. Based on the observed pattern, we estimate the amount of discharge energy converted to heat during the discharge time: the rate of temperature increase is in the order of several degrees K per nanosecond.