fatal: ‘heroku’ does not appear to be a git repository

I was facing same issues, When i cloned a client project and he had already created heroku server. Even he collaborated me to his account.

Below googled solution worked for me.

git remote add heroku git@heroku.com:appname.git

Where appname is the name of your app.

After that

git push heroku master

(assuming you want to push the master branch)