FWIW my heartbeat canister (which doesn’t do inter-canister calls) burns around 90 B cycles every 12 hours, so roughly 0.18 T cycles every 24 hours.
This is lower than @PaulLiu’s tip jar canister, which apparently burns ~0.5 T cycles every 24 hours.
I guess it also depends on how much work is being done in your heartbeat function.