I'm thinking this produce a bit more of a complete list...

# repoquery --resolve --whatrequires fltk
rpmdb: /var/lib/rpm/Name: unexpected file type or format
error: cannot open Name index using db3 - Invalid argument (22)
rpmdb: /var/lib/rpm/Providename: unexpected file type or format
error: cannot open Providename index using db3 - Invalid argument (22)
fltk-0:1.1.10-1.el6.x86_64
fltk-0:1.1.10-1.el6.i686
Pixie-0:2.2.6-3.el6.i686
Pixie-0:2.2.6-3.el6.x86_64
alsamixergui-0:0.9.0-0.9.rc2.el6.x86_64
aqsis-0:1.6.0-3.el6.x86_64
aqsis-libs-0:1.6.0-3.el6.i686
aqsis-libs-0:1.6.0-3.el6.x86_64
fltk-devel-0:1.1.10-1.el6.i686
fltk-devel-0:1.1.10-1.el6.x86_64
fltk-fluid-0:1.1.10-1.el6.x86_64
htmldoc-0:1.8.27-13.el6.x86_64
mup-0:6.1-4.el6.x86_64
octave-6:3.4.3-1.el6.i686
octave-6:3.4.3-1.el6.x86_64
rakarrack-0:0.5.8-2.el6.x86_64

Richard