hard and fast enough that your heart could not start back up?
Actually the hard and fast part isn’t necessary. A rather soft blow by a ball in exactly the right time and place on your chest can and will cause your heart to get out of rhythm.
It is called Commotio Cordis and many people have died from it.
Err, I’m pretty sure if you get hit hard and fast enough at any point during the heartbeat cycle your heart can stop…or get pulverized into mist.
I guess if you are asking if there is an unusually “low” amount of force that can be applied during specific times in the heart beat cycle to cause a disruption of the cycle.
The answer is yes, there is. See here
thanks, interesting reading.