VBA Heroku integration?
Number of options here depending on how you want to connect. I would consider exposing an API in your Heroku app that your VBA could consume (if possible).
Failing that;
The present Shared Database won't let you connect directly to the database so that's a no no.
The new beta shared postgres 9.1 (https://postgres.heroku.com/blog/past/2012/4/26/heroku_postgres_development_plan/) will let you connect to it from outside.
Use one of the Heroku DB addon providers such as ClearDB which is a mySQL provider which allows direct access to the database.
Bring your own database which you could host on an external server and have your Heroku app connected to it (watch out for latency) and then you can connect your printing app directly to that Db.