We have constructed high-order T = 0 expansions for the elementary excitation spectra, and high temperature expansions for the susceptibility, for the S = 1/2 Heisenberg antiferromagnet believed to describe the spin-gap system CaV4O9. Existing susceptibility data are analyzed using these theoretical results. If nearest- and second-neighbor interactions are in the ratio 2:1, there should be clear indications in both neutron and Raman Scattering.