@Override
        public String toStringBase() {
            return super.toStringBase() +
                    ", remainingMs=" + heartbeatTimer.remainingMs() +
                    ", heartbeatIntervalMs=" + heartbeatIntervalMs;
        }
The heartbeat interval which is acquired/updated through the heartbeat request
clients/src/main/java/org/apache/kafka/clients/consumer/internals/HeartbeatRequestManager.java