The Linux-HA project maintains a set of building blocks for high availability cluster systems, including a cluster messaging layer, a huge number of resource agents for a variety of applications, and a plumbing library and error reporting toolkit.

You usually want to deploy the Pacemaker Cluster Resource Manager on top of the Heartbeat infrastructure layer. If you happen to be still under the impression that this CRM would be part of Heartbeat, please see Why was the Pacemaker Project Created?