  We present low temperature Raman spectra of $NaV_2O_5$ single crystal. The
assignation of the observed modes is done on the basis of Monte Carlo
calculation of excited states of Heisenberg dimerized Hamiltonian, without
frustration. We found a good agreement between measured and calculated magnetic
excitations for $\delta=0.048$ and $J=452 K$. The singlet-triplet,
singlet-singlet excitations as well as two-magnon mode are observed to be at
66, 127 and 132 cm^{-1}.
