What's a good iPhone running app with a heart rate monitor? I'm looking for a combination of an app like RunKeeper that tracks my running speed, with an app (+hardware?) to track my heart rate.

I'm currently running with RunKeeper (to track my speed) and also wearing an chestband+wristwatch (to track my heart rate). It would be nice to get rid of the wristwatch, if there's some app (and chestband receiver hardware?) to combine the data.

I've seen some apps that only do heart rate monitoring, but I don't want to switch between 2 apps while running.
There is Digifit which is software that works with any ANT+ enabled devices by brand names such as Adidas, Garmin, StarTrac and Timex.