I have written something that hook into WordPress' heartbeat via the heartbeat-send
JS event.
However, to test things I am doing a lot of sitting around and waiting.
I've tried to run jQuery(document).trigger("heartbeat-send");
from the console with no luck.
I'm unsure of how to trigger the heartbeat at any time, or if it's even possible :)
Was just looking for this myself and came across this answer on another site to manually trigger the heartbeat: