Investigations of different superconducting (S)/ferromagnetic (F) heterostructures grown by pulsed laser deposition reveal that the activation energy (U) for the vortex motion in a high T(c) superconductor is reduced remarkably by the presence of F layers. The U exhibits a logarithmic dependence on the applied magnetic field in the S/F bilayers suggesting the existence of decoupled two-dimensional (2D) pancake vortices. This result is discussed in terms of the reduction in the effective S layer thickness and the weakening of the S coherence length due to the presence of F layers. In addition, the U and the superconducting T(c) in Y Ba(2)Cu(3)O(7 - δ)/La(0.5)Sr(0.5)CoO(3) bilayers are observed to be much lower than in the Y Ba(2)Cu(3)O(7 - δ)/La(0.7)Sr(0.3)MnO(3) ones. This in turn suggests that the degree of spin polarization of the F layer might not play a crucial role for the suppression of superconductivity due to a spin polarized induced pair-breaking effect in S/F bilayers.