Log the act of sending a heartbeat (DEBUG level).

rq/worker.py

@@ -343,6 +343,9 @@ class Worker(object):
                 return Queue.dequeue_any(self.queues, timeout,
                         connection=self.connection)
             except DequeueTimeout:
+                pass
+
+            self.log.debug('Sending heartbeat to prevent worker timeout.')
             self.connection.expire(self.key, self.default_worker_ttl)