  The possibility of a heavy supersymmetric spectrum at the Minimal
Supersymmetric Standard Model is considered and the decoupling from the low
energy electroweak scale is analyzed in detail. The formal proof of decoupling
of supersymmetric particles from low energy physics is stated in terms of the
effective action for the particles of the Standard Model that results by
integrating out all the sparticles in the limit where their masses are larger
than the electroweak scale. The computation of the effective action for the
standard electroweak gauge bosons W^{+-}, Z and \gamma is performed by
integrating out all the squarks, sleptons, charginos and neutralinos to
one-loop. The Higgs sector is not considered in this paper. The large sparticle
masses limit is also analyzed in detail. Explicit analytical formulae for the
two-point functions of the electroweak gauge bosons to be valid in that limit
are presented. Finally, the decoupling of sparticles in the S, T and U
parameters is studied analitically. A discussion on how the decoupling takes
place in terms of both the physical sparticle masses and the non-physical mass
parameters as the \mu-parameter and the soft-breaking parameters is included.
