The hippocampal CA3 region plays an important role in learning and memory. CA3 pyramidal neurons (PNs) receive two prominent excitatory inputs - mossy fibers (MFs) from dentate gyrus (DG) and recurrent collaterals (RCs) from CA3 PNs - that play opposing roles in pattern separation and pattern completion, respectively. Although the dorsoventral heterogeneity of the hippocampal anatomy, physiology, and behavior has been well established, nothing is known about the dorsoventral heterogeneity of synaptic connectivity in CA3 PNs. In this study, we performed Timm's sulfide silver staining, dendritic and spine morphological analyses, and ex vivo electrophysiology in mice of both sexes to investigate the heterogeneity of MF and RC pathways along the CA3 dorsoventral axis. Our morphological analyses demonstrate that ventral CA3 (vCA3) PNs possess greater dendritic lengths and more complex dendritic arborization, compared to dorsal CA3 (dCA3) PNs. Moreover, using ChannelRhodopsin2 (ChR2)-assisted patch-clamp recording, we find that the ratio of the RC-to-MF excitatory drive onto CA3 PNs increases substantially from dCA3 to vCA3, with vCA3 PNs receiving significantly weaker MFs, but stronger RCs, excitation than dCA3 PNs. Given the distinct roles of MF versus RC inputs in pattern separation versus completion, our findings of the significant dorsoventral variations of MF and RC excitation in CA3 PNs may have important functional implications for the contribution of CA3 circuit to the dorsoventral difference in hippocampal function.Significance Statement The hippocampal CA3 region is essential for memory formation. CA3 pyramidal neurons receive recurrent collateral (RC) from CA3 and mossy fiber (MF) from dentate gyrus (DG), which have opposite functions in pattern completion (memory generalization) and separation (discrimination), respectively. Although hippocampal dorsoventral heterogeneity is well established, dorsoventral heterogeneity of CA3 connectivity is unknow. Here, we demonstrate that the ratio of RC-to-MF excitation increases substantially from dCA3 to vCA3, with vCA3 receiving significantly weaker MF, but stronger RC, excitation than dCA3. Thus, our study reveals a novel CA3-based synaptic mechanism that may offer the computational advantage for the ventral hippocampus to be more strongly involved in behaviors that require less precision but more generalization than the dorsal hippocampus.