A heartbeat implies conformance, repeatability, closure. Think about what happens, for a minute, when the human heart beats:
- the heart expands, allowing blood in
- the heart squeezes, moving the blood around inside the heart
- the heart squeezes differently, moving the blood out of the heart into the body
- during all this, the valves of the heart open and close
(I'll note I'm definitely NOT a doctor.)
When a heart does things in a kinda sorta way, you've got a problem. A leaky heart valve, that's a problem. A heart that doesn't pump all the blood through, that's a problem. These are inefficiencies in the human heart, and when they get bad enough then you're in serious trouble.
The same thing is true of a development project. We don't create and maintain a project heartbeat because it feels good. We do it because if we don't have rhythm then we're showing ineffficiencies and when those get bad enough then we're in serious trouble. For example, if our stories no longer fit in an iteration, that's a leak. Once or twice is okay, but if it happens a lot or badly, then the project is in trouble, and we're likely to be late or broken, or both.
Don't have a project heart attack. Keep an eye on your project's heartbeat.