I would check into the port you are using. On a normal ubuntu machine for example you may have to use sudo for low numbered ports (such as port 80). Besides that Heroku has a lot of load balancing going on, so the port you will use to connect to the service may not be the same as the port you tell the instance to listen on.
I would try using port 5000 as per this example from Heroku Nodejs with sockets