Steps to Reproduce:
1. Open up a world and run

/summon minecraft:warden ~ ~ ~ {Health:0f,DeathTime:-200s}

Command courtesy of Avoma

Original Description:

If you were to kill a warden, its heartbeat still continues to happen even in the death animation.

To replicate this, pay attention to the frequency of the warden's heartbeat and time it so the next one would align to killing it and being in its death animation. You will see that it will continue to beat even during the death animation and can be confirmed further by turning subtitles on. This way you can see the "Warden's Heart Beats" plays after "Warden Dies" as well as seeing that the warden's heart visually beat on its chest during death animation.