avtaniket

Suppose you have two heroku remote apps
myapp-dev & myapp-prod
and two git branches 
master(for dev) & production
Now lets setup heroku on the existing git repo in your local machine
Assuming the branches and the apps exist already
git remote add heroku-myapp-dev https://git.heroku.com/myapp-dev.git 
git remote add heroku-myapp-prod https://git.heroku.com/myapp-prod.git