diff --git a/rhodecode/lib/hooks_utils.py b/rhodecode/lib/hooks_utils.py
--- a/rhodecode/lib/hooks_utils.py
+++ b/rhodecode/lib/hooks_utils.py
@@ -80,7 +80,7 @@ def trigger_log_create_pull_request_hook
     extras = _get_rc_scm_extras(username, repo_name, repo_alias,
                                 'create_pull_request')
     events.trigger(events.PullRequestCreateEvent(pull_request))
-    extras.update(pull_request.get_api_data())
+    extras.update(pull_request.get_api_data(with_merge_state=False))
     hooks_base.log_create_pull_request(**extras)
 
 
diff --git a/rhodecode/lib/vcs/backends/base.py b/rhodecode/lib/vcs/backends/base.py
--- a/rhodecode/lib/vcs/backends/base.py
+++ b/rhodecode/lib/vcs/backends/base.py
@@ -161,7 +161,7 @@ class MergeResponse(object):
             u'This pull request cannot be merged because the source contains '
             u'more branches than the target.'),
         MergeFailureReason.HG_TARGET_HAS_MULTIPLE_HEADS: lazy_ugettext(
-            u'This pull request cannot be merged because the target '
+            u'This pull request cannot be merged because the target `{target_ref.name}` '
             u'has multiple heads: `{heads}`.'),
         MergeFailureReason.TARGET_IS_LOCKED: lazy_ugettext(
             u'This pull request cannot be merged because the target repository is '
@@ -309,6 +309,9 @@ class BaseRepository(object):
     def _remote(self):
         raise NotImplementedError
 
+    def _heads(self, branch=None):
+        return []
+
     @LazyProperty
     def EMPTY_COMMIT(self):
         return EmptyCommit(self.EMPTY_COMMIT_ID)
diff --git a/rhodecode/lib/vcs/backends/hg/repository.py b/rhodecode/lib/vcs/backends/hg/repository.py
--- a/rhodecode/lib/vcs/backends/hg/repository.py
+++ b/rhodecode/lib/vcs/backends/hg/repository.py
@@ -715,11 +715,16 @@ class MercurialRepository(BaseRepository
 
         try:
             if target_ref.type == 'branch' and len(self._heads(target_ref.name)) != 1:
-                heads = ','.join(self._heads(target_ref.name))
+                heads = '\n,'.join(self._heads(target_ref.name))
+                metadata = {
+                    'target_ref': target_ref,
+                    'source_ref': source_ref,
+                    'heads': heads
+                }
                 return MergeResponse(
                     False, False, None,
                     MergeFailureReason.HG_TARGET_HAS_MULTIPLE_HEADS,
-                    metadata={'heads': heads})
+                    metadata=metadata)
         except CommitDoesNotExistError:
             log.exception('Failure when looking up branch heads on hg target')
             return MergeResponse(
diff --git a/rhodecode/model/pull_request.py b/rhodecode/model/pull_request.py
--- a/rhodecode/model/pull_request.py
+++ b/rhodecode/model/pull_request.py
@@ -1317,8 +1317,16 @@ class PullRequestModel(BaseModel):
             possible = pull_request.last_merge_status == MergeFailureReason.NONE
             metadata = {
                 'target_ref': pull_request.target_ref_parts,
-                'source_ref': pull_request.source_ref_parts
+                'source_ref': pull_request.source_ref_parts,
             }
+            if not possible and target_ref.type == 'branch':
+                # NOTE(marcink): case for mercurial multiple heads on branch
+                heads = target_vcs._heads(target_ref.name)
+                if len(heads) != 1:
+                    heads = '\n,'.join(target_vcs._heads(target_ref.name))
+                    metadata.update({
+                        'heads': heads
+                    })
             merge_state = MergeResponse(
                 possible, False, None, pull_request.last_merge_status, metadata=metadata)
 
diff --git a/rhodecode/tests/models/test_pullrequest.py b/rhodecode/tests/models/test_pullrequest.py
--- a/rhodecode/tests/models/test_pullrequest.py
+++ b/rhodecode/tests/models/test_pullrequest.py
@@ -512,7 +512,7 @@ def test_outdated_comments(
     (MergeFailureReason.HG_SOURCE_HAS_MORE_BRANCHES,
      'This pull request cannot be merged because the source contains more branches than the target.'),
     (MergeFailureReason.HG_TARGET_HAS_MULTIPLE_HEADS,
-     'This pull request cannot be merged because the target has multiple heads: `a,b,c`.'),
+     'This pull request cannot be merged because the target `ref_name` has multiple heads: `a,b,c`.'),
     (MergeFailureReason.TARGET_IS_LOCKED,
      'This pull request cannot be merged because the target repository is locked by user:123.'),
     (MergeFailureReason.MISSING_TARGET_REF,