We use Heartbeat (and DRBD) in two products. The first is the CUDA 12000 IP Access Switch. This is a Cable Modem Termination System (CMTS) which uses Linux for service provisioning and network management.
From the web page: Contains integrated service provisioning and element/network management functions eliminating the need for separate systems while capitalizing on the high availability Linux-based management module.
The second product is the FastFlow Broadband Provisioning Manager. The FBPM provides the same provisioning services that are available on the Cuda 12000 on a stand alone Linux platform.