Using an operator product expansion (OPE) in the inverse of the heavy quark massM Q and a dispersive approach, we rederive theB andB * couplings and the Isgur-Wise function predicted by the infinite mass effective theory (IMET). We find that, at the subtraction pointM Q and using VDM for the spectral function, these observables are governed by the universal $$\left\langle {\bar qq} \right\rangle $$ light quark condensate. We also find that the corrections induced by finite values ofM c andM b are large and are due to the splitting Δb between the ground state and its radial excitation. We review the determinations of the different decay constants, couplings and masses from QCD spectral sum rules (QSSR). Forf B andf D , we conclude the optimum average:f B =(1.59±0.09±0.27)f π andf D =(1.31±0.12)f π, where the main error is due to the quark mass, while the first one inf B is due to the non-perturbative terms and to the choice of the continuum thresholdt c from the onset of sum rule variable stability until thet c -stability regions. We also find that the vector coupling γV satisfies approximately the IMETM Q 3/2 mass dependence scaling law, whilef P obeys in units of GeV:f P/fπ≅(4.6±0.4)M Q −1/2 (1–1.56/M Q +0.88/M Q 2 ), forM Q ≥M c . We also predict the flavour independence:M P -M Q ≅0.6-0.7 GeV andM V -M Q ≅0.7-0.8 GeV of the mass differences between the mesons and the corresponding quark. Finally we find that theB→Dev e form factorf +(0)≅(0.55±0.10) deviates from the naive expectation (f +(0)=1).