diff --git a/rq/scheduler.py b/rq/scheduler.py
index 97d627cc..175f6078 100644
--- a/rq/scheduler.py
+++ b/rq/scheduler.py
@@ -171,24 +171,24 @@ class RQScheduler:
     def heartbeat(self):
         """Updates the TTL on scheduler keys and the locks"""
         self.log.debug('Scheduler sending heartbeat to %s', ', '.join(self.acquired_locks))
-        if len(self._queue_names) > 1:
+        if len(self._acquired_locks) > 1:
             with self.connection.pipeline() as pipeline:
                 for name in self._acquired_locks:
                     key = self.get_locking_key(name)
                     pipeline.expire(key, self.interval + 60)
                 pipeline.execute()
-        else:
-            key = self.get_locking_key(next(iter(self._queue_names)))
+        elif self._acquired_locks:
+            key = self.get_locking_key(next(iter(self._acquired_locks)))
             self.connection.expire(key, self.interval + 60)
 
     def stop(self):
-        self.log.info('Scheduler stopping, releasing locks for %s...', ', '.join(self._queue_names))
+        self.log.info('Scheduler stopping, releasing locks for %s...', ', '.join(self._acquired_locks))
         self.release_locks()
         self._status = self.Status.STOPPED
 
     def release_locks(self):
         """Release acquired locks"""
-        keys = [self.get_locking_key(name) for name in self._queue_names]
+        keys = [self.get_locking_key(name) for name in self._acquired_locks]
         self.connection.delete(*keys)
         self._acquired_locks = set()
 
diff --git a/tests/test_scheduler.py b/tests/test_scheduler.py
index 8aa722a4..e6edf725 100644
--- a/tests/test_scheduler.py
+++ b/tests/test_scheduler.py
@@ -204,6 +204,33 @@ class TestScheduler(RQTestCase):
             self.assertEqual(mocked.call_count, 1)
             self.assertEqual(stopped_process.is_alive.call_count, 1)
 
+    def test_lock_release(self):
+        """Test that scheduler.release_locks() only releases acquired locks"""
+        name_1 = 'lock-test-1'
+        name_2 = 'lock-test-2'
+        scheduler_1 = RQScheduler([name_1], self.testconn)
+
+        self.assertEqual(scheduler_1.acquire_locks(), {name_1})
+        self.assertEqual(scheduler_1._acquired_locks, {name_1})
+
+        # Only name_2 is returned since name_1 is already locked
+        scheduler_1_2 = RQScheduler([name_1, name_2], self.testconn)
+        self.assertEqual(scheduler_1_2.acquire_locks(), {name_2})
+        self.assertEqual(scheduler_1_2._acquired_locks, {name_2})
+
+        self.assertTrue(self.testconn.exists(scheduler_1.get_locking_key(name_1)))
+        self.assertTrue(self.testconn.exists(scheduler_1_2.get_locking_key(name_1)))
+        self.assertTrue(self.testconn.exists(scheduler_1_2.get_locking_key(name_2)))
+
+        scheduler_1_2.release_locks()
+
+        self.assertEqual(scheduler_1_2._acquired_locks, set())
+        self.assertEqual(scheduler_1._acquired_locks, {name_1})
+
+        self.assertTrue(self.testconn.exists(scheduler_1.get_locking_key(name_1)))
+        self.assertTrue(self.testconn.exists(scheduler_1_2.get_locking_key(name_1)))
+        self.assertFalse(self.testconn.exists(scheduler_1_2.get_locking_key(name_2)))
+
     def test_queue_scheduler_pid(self):
         queue = Queue(connection=self.testconn)
         scheduler = RQScheduler(
@@ -219,25 +246,33 @@ class TestScheduler(RQTestCase):
         """Test that heartbeat updates locking keys TTL"""
         name_1 = 'lock-test-1'
         name_2 = 'lock-test-2'
-        scheduler = RQScheduler([name_1, name_2], self.testconn)
+        name_3 = 'lock-test-3'
+        scheduler = RQScheduler([name_3], self.testconn)
+        scheduler.acquire_locks()
+        scheduler = RQScheduler([name_1, name_2, name_3], self.testconn)
         scheduler.acquire_locks()
 
         locking_key_1 = RQScheduler.get_locking_key(name_1)
         locking_key_2 = RQScheduler.get_locking_key(name_2)
+        locking_key_3 = RQScheduler.get_locking_key(name_3)
 
         with self.testconn.pipeline() as pipeline:
             pipeline.expire(locking_key_1, 1000)
             pipeline.expire(locking_key_2, 1000)
+            pipeline.expire(locking_key_3, 1000)
+            pipeline.execute()
 
         scheduler.heartbeat()
         self.assertEqual(self.testconn.ttl(locking_key_1), 61)
-        self.assertEqual(self.testconn.ttl(locking_key_1), 61)
+        self.assertEqual(self.testconn.ttl(locking_key_2), 61)
+        self.assertEqual(self.testconn.ttl(locking_key_3), 1000)
 
         # scheduler.stop() releases locks and sets status to STOPPED
         scheduler._status = scheduler.Status.WORKING
         scheduler.stop()
         self.assertFalse(self.testconn.exists(locking_key_1))
         self.assertFalse(self.testconn.exists(locking_key_2))
+        self.assertTrue(self.testconn.exists(locking_key_3))
         self.assertEqual(scheduler.status, scheduler.Status.STOPPED)
 
         # Heartbeat also works properly for schedulers with a single queue