The paper investigates the prescribed-time formation tracking control problem of heterogeneous linear multi-agent systems with a dynamic leader. To achieve this, a class of sensory-feedback prescribed-time distributed observers is designed for followers to cooperatively estimate the state information of the leader, based on which a prescribed-time controller is further proposed to achieve the output formation tracking of the leader. Notably, the design of the distributed observer for each agent only relies on the local output measurements of its neighboring agents, which eliminates the necessity of direct communication among the agents and thus enhances the practical significance of the research problem while introduces technical challenges. By utilizing coordinate transformation based on output regulation method, the output formation tracking control of heterogeneous linear multi-agent systems is converted into an equivalent stabilization problem. Based on the Lyapunov and prescribed-time stability theory, it is shown that the leader-follower formation tracking control of the heterogeneous multi-agent systems is achieved in a prescribed time, which is independent of the initial states and the control parameters of the multi-agent system can be arbitrarily chosen. Finally, simulation results demonstrate the effectiveness of the proposed method.