Modified Bloch equations were used to simulate the solution EPR spectra of mixed-valence heteropolyanions containing vanadium(IV) and vanadium(V). Simulated are the 15-, 22-, 36- and 43-line spectra of $alpha$-1,2-$[PV(IV)VW_{10})O_{40}]^{6-},;[P_2V(IV)V_2W_{15}O_{62}]^{10-},;[HP_2V(IV)V_2W_{15}O_{62}]^{9-}$ and $alpha$-1,2,3-$[HSiV(IV)V_2W_9O_{40}]^{7-}$, respectively. The transition probabilities for the intramolecular electron transfer were determined from the simulations.