Have you tried looking at: http://www.codeproject.com/KB/WCF/WCF_Duplex_UI_Threads.aspx
Can you provide examples of what you have already attempted? With details of firewalls etc, error messages?
If both client and server can be addressed directly and firewalls are not an issue, have you considered allowing clients to register a URL providing a supported contract. The server can then call this service whenever it needs to, without the need to establish a long running (but mostly idle connection), avoids the need for heart beating and can be made resilient across sessions\connections.
