This paper addresses the cooperative output regulation problem of heterogeneous linear multi-agent systems with directed communication topologies, requiring only intermittent communication. First, we propose a unified framework of time- and event-triggering strategies. Then based on the unified triggering framework, a novel triggering mechanism utilizing the self-triggering strategy is developed. It is shown that with the proposed triggering mechanism, the cooperative output regulation problem can be solved by a distributed control law with only intermittent communication. It is further shown that with the unified framework of time- and event-triggering strategies for each agent, a positive minimum inter-event time can be explicitly given and Zeno behavior can be thus excluded. An example is finally provided to demonstrate the effectiveness of the proposed controller and the triggering mechanism.