Heartbeats are not serviced with a desired frequency set by heartbeat.interval.ms configuration property.

In the case of binlog-based connectors, heartbeats are serviced here and attached to the binlog client via client.registerEventListener call here  This means that if there are no change events in the heartbeat.interval.ms time interval, there will no be heartbeat generated.

For SQL Server it's a bit different, there is a sleeper here that sleeps for poll.interval.ms if there are no db changes; if heartbeat.interval.ms < poll.interval.ms then heartbeats will be generated with poll.interval.ms frequency instead of heartbeat.interval.ms frequency.

Heartbeat implementation is highly coupled to change event processing and as a result I propose we simply document this behavior in the official docs.