Let $f$ be the gluing map of a Heegaard splitting of a 3-manifold $W$. The goal of this paper is to determine the information about $W$ contained in the image of $f$ under the symplectic representation of the mapping class group. We prove three main
results. First, we show that the first homology group of the three manifold together with Seiferts linking form provides a complete set of stable invariants. Second, we give a complete, computable set of invariants for these linking forms. Third, we show that a slight augmentation of Birmans determinantal invariant for a Heegaard splitting gives a complete set of unstable invariants.
