The heartbeat does not affect the ports or connections. It just sends a msg to the alt lobbies every 30 seconds or so. Also does not affect the official NW lobbies or anything. It is completely passive.
You can use this web tool to try and ping your server externally. If the ports and router are configured correctly you'll get a response with some info about the game. If there is a problem with your ports or a firewall blocking access it won't be able to connect and you'll get a STATUS: OFFLINE message.
Select Black Hawk Down, enter the IP:Port like 207.178.209.215:17479
http://nw.novahq.net/nova/ping