Network Heartbeat / TCP/IP sub-protocol sets START / STOP and TIME TO LIVE of a stock market flash trade session then notifies next user of available trade window. Sync Delta heartbeat message activities send alerts of threshold activity to alert then halt runaway trade activity. The Heartbeat is an opportunity in time to get / put data and time stamp that data -- the only one.  All sophisticated algorithms, bots, mots, scripts, agents.. make calls to the Heartbeat primative.  High frequency trade algorithms are sophisticated and distributed. The network / device heartbeat is omnipresent and simply powerful -- algorithm on / algorithm off.