This paper analyzes a security market with sequential trade and a specialist dealer. I study how heterogeneous Bayes-rational agents with private signals interact if allowed to decide multiple times. I show that in this setting, informational cascades can occur. That is, all agents choose to follow public information over their private signal. I introduce a shortselling constraint on the dealer side, i.e. finite supply of the traded asset. When this constraint binds, cascades can be terminated endogenously in the model.