  Recent high resolution observations by the {\it Chandra} X-ray satellite
revealed various substructures in hot X-ray emitting plasmas in cluster of
galaxies. For example, {\it Chandra} revealed the existence of sharp
discontinuities in the surface brightness at the leading edge of subclusters in
merging clusters (e.g., Abell 3667), where the temperature drops sharply across
the fronts. These sharp edges are called cold fronts. We present results of
three-dimensional (3D) magnetohydrodynamic simulations of the interaction
between a dense subcluster plasma and ambient magnetized intracluster medium.
Anisotropic heat conduction along magnetic field lines is included. At the
initial state, magnetic fields are assumed to be uniform and transverse to the
motion of the dense subcluster. Since magnetic fields ahead of the subcluster
slip toward the third direction in the 3D case, the strength of magnetic fields
in this region can be reduced compared to that in the 2D case. Nevertheless, a
cold front can be maintained because the magnetic field lines wrapping around
the forehead of the subcluster suppress the heat conduction across them. On the
other hand, when the magnetic field is absent, a cold front cannot be
maintained because isotropic heat conduction from the hot ambient plasma
rapidly heats the cold subcluster plasma.
