knocked out by a blow to the heart

He first made a cross counter, just as Accelerator had expected. Aiming for the center of
the chest rather than the face was certainly out of the ordinary, but it was within the range
of options he could take with that fist.
The problem was what came later.
Kamijou swung up the baby head rock with his left hand.
He first neutralized the reflection with his right hand and then he applied a tremendous
force to Accelerator’s heart, even if it meant crushing his own right fist in the process. The
impact from the rock was much greater than anything he could have caused with a mere
fist.
(Ah.)
Accelerator’s mind went blank.
With a tremendous noise, the thoughts that controlled his calculations cut out for an
instant.

- New Testament Volume 10 Chapter 9 Part 5