diff --git a/changelog/fix_style_redundant_self_assignment_branch_to_handle_heredocs.md b/changelog/fix_style_redundant_self_assignment_branch_to_handle_heredocs.md
new file mode 100644
index 000000000000..1b363a0b6449
--- /dev/null
+++ b/changelog/fix_style_redundant_self_assignment_branch_to_handle_heredocs.md
@@ -0,0 +1 @@
+* [#12133](https://github.com/rubocop/rubocop/pull/12133): Fix `Style/RedundantSelfAssignmentBranch` to handle heredocs. ([@r7kamura][])
diff --git a/lib/rubocop/cop/style/redundant_self_assignment_branch.rb b/lib/rubocop/cop/style/redundant_self_assignment_branch.rb
index cb0aec73bd1c..3340094e0606 100644
--- a/lib/rubocop/cop/style/redundant_self_assignment_branch.rb
+++ b/lib/rubocop/cop/style/redundant_self_assignment_branch.rb
@@ -75,6 +75,11 @@ def register_offense(if_node, offense_branch, opposite_branch, keyword)
           add_offense(offense_branch) do |corrector|
             assignment_value = opposite_branch ? opposite_branch.source : 'nil'
             replacement = "#{assignment_value} #{keyword} #{if_node.condition.source}"
+            if opposite_branch.respond_to?(:heredoc?) && opposite_branch.heredoc?
+              replacement += opposite_branch.loc.heredoc_end.with(
+                begin_pos: opposite_branch.source_range.end_pos
+              ).source
+            end
 
             corrector.replace(if_node, replacement)
           end
diff --git a/spec/rubocop/cop/style/redundant_self_assignment_branch_spec.rb b/spec/rubocop/cop/style/redundant_self_assignment_branch_spec.rb
index 9b57e2313532..0c63eafc769e 100644
--- a/spec/rubocop/cop/style/redundant_self_assignment_branch_spec.rb
+++ b/spec/rubocop/cop/style/redundant_self_assignment_branch_spec.rb
@@ -93,6 +93,25 @@
     RUBY
   end
 
+  it 'registers and corrects an offense when self-assigning redundant if branch with heredoc' do
+    expect_offense(<<~RUBY)
+      foo = if condition
+              foo
+              ^^^ Remove the self-assignment branch.
+            else
+              <<~TEXT
+                bar
+              TEXT
+            end
+    RUBY
+
+    expect_correction(<<~RUBY)
+      foo = <<~TEXT unless condition
+                bar
+              TEXT
+    RUBY
+  end
+
   it 'does not register an offense when self-assigning redundant else branch and multiline if branch' do
     expect_no_offenses(<<~RUBY)
       foo = if condition