  We analyse the 2010 April 3rd CME using spacecraft coronagraphic images at
different vantage points (SOHO, STEREO-A and STEREO-B). We perform a 3D
reconstruction of both the flux rope and shock using the Graduated Cylindrical
Shell (GCS) model to calculate CME kinematic and morphologic parameters (e.g.
velocity, acceleration, radius). The obtained results are fitted with empirical
models describing the expansion of the CME radius in the heliosphere and
compared with in situ measurements from Wind spacecraft: the CME is found to
expand linearly towards Earth. Finally, we relate the event with decreases in
the Galactic Cosmic Ray (GCR) Flux, known as Forbush decreases (FD), detected
by EPHIN instrument onboard SOHO spacecraft. We use the analytical
diffusion-expansion model (ForbMod) to calculate the magnetic field power law
index, obtaining a value of approximately 1.6, thus estimating a starting
magnetic field of around 0.01 G and an axial magnetic flux of around 5x1E20 Mx
at 15.6 Rsun.
