A study of the interaction of interplanetary shock waves with the heliospheric current sheet/heliospheric plasma sheet (HCS/HPS) and the disturbed flow behind them is made with a 2.5 dimensional MHD code that uses improved computational techniques. The aim is to determine if such interactions for typical shocks can produce sufficiently large changes in the interplanetary plasma and field to be geoeffective. The mutual interaction of the shock-waves with the HCS/HPS is examined for several angles between the shock normal and the HCS/HPS. We separate the effects of the HCS from those due to angular distance of observer from the initial shock center. The shocks are initiated at 0.1 AU by a finite-duration increase in initial radial velocity. We examine the transit times of the resultant shocks to 1-AU and their strengths along their peripheries. We also examine the 1-AU signatures of the polar component of the magnetic field, B&thgr;, in the interplanetary disturbance at and following the leading fastmode MHD shock. Note that B&thgr;=-Bz. We show the differences that result from the presence of the HCS, both qualitatively and quantitatively. The largest effects occur in B&thgr;, which reaches its largest excursions within 10¿ of the edge of the HPS. For the moderate shocks simulated in this study, deflections of the field lines produce values of B&thgr; between 4 and 5 nT in the presence of a HCS. These values are at the lower end of the range considered necessary for interplanetary events to initiate moderate geomagnetic storms. Further study is required to investigate the nature of input pulses and HCS that would give larger B&thgr; variations. ¿ 1998 American Geophysical Union