if you're using the heroku-deploy step (this step is injected if a Heroku deploy target is used) you don't have to specify your api key and app name twice just use the $HEROKU_KEY and $HEROKU_APP_NAME vars
Example from https://github.com/wwwouter/failing-getting-started-nodejs
box: wercker/nodejs
build:
steps:
- script:
code: echo Building
deploy:
steps:
- heroku-deploy
passed-steps:
- script:
name: waiting before checking heroku log
code: sleep 60
- wouter/check-heroku-log:
api-key: $HEROKU_KEY
app-name: $HEROKU_APP_NAME