  We compare two widely used approaches to the description of hadron
properties: QCD sum rules and constituent quark models. Making use of the
dispersion formulation of the quark model, we show that both approaches lead to
similar spectral representations for hadron observables with an important
difference that quark model is based on Feynman diagrams with massive quarks,
whereas QCD sum rules are based on the same Feynman diagrams for current quarks
with the additional condensate contributions for light quarks and gluons. We
give arguments for a similarity of the smearing function in sum rules and the
hadron wave function of the quark model. Analyzing the sum rule for the
leptonic decay constant of the heavy pseudoscalar meson containing a light $u$
or $s$ quark, we find that the quark condensates at the chiral
symmetry-breaking scale $\mu_\chi\simeq 1$ GeV, $<\bar u u > = - (230 \pm 15
{\rm MeV})^3$ and $<\bar s s > = - (220 \pm 15 {\rm MeV})^3$ correspond to
constituent quark masses $m_u\simeq 220$ MeV and $m_s \simeq 350$ MeV,
respectively. We also obtain the running of the quark model parameters above
the chiral scale $\mu_\chi$. The observed correspondence between constituent
quark models and QCD sum rules allows a deeper understanding of both methods
and their parameters. It also provides a QCD basis for constituent quark
models, extending their applicability above the scale of chiral symmetry
breaking.
