emerge -vt kde-base/arts
>>> --tree implies --pretend... adding --pretend to options.

These are the packages that would be merged, in reverse order:

Calculating dependencies... done!
[blocks B     ] >=kde-base/kdelibs-3.5.4-r2 (is blocking kde-base/kde-env-3-r4)
[ebuild   R   ] kde-base/arts-3.5.5  USE="alsa arts%* mp3 vorbis xinerama -artswrappersuid -debug -esd -jack -kdeenablefinal -nas" 0 kB 
[ebuild  N    ]  kde-base/kde-env-3-r4  0 kB