diff --git a/opencodeblocks/blocks/codeblock.py b/opencodeblocks/blocks/codeblock.py
index ae8c9fc1..87619798 100644
--- a/opencodeblocks/blocks/codeblock.py
+++ b/opencodeblocks/blocks/codeblock.py
@@ -82,14 +82,16 @@ def init_run_button(self):
         """Initialize the run button"""
         run_button = QPushButton(">", self.root)
         run_button.move(int(self.edge_size), int(self.edge_size / 2))
-        run_button.setFixedSize(int(3 * self.edge_size), int(3 * self.edge_size))
+        run_button.setFixedSize(int(3 * self.edge_size),
+                                int(3 * self.edge_size))
         run_button.clicked.connect(self.run_left)
         return run_button
 
     def init_run_all_button(self):
         """Initialize the run all button"""
         run_all_button = QPushButton(">>", self.root)
-        run_all_button.setFixedSize(int(3 * self.edge_size), int(3 * self.edge_size))
+        run_all_button.setFixedSize(
+            int(3 * self.edge_size), int(3 * self.edge_size))
         run_all_button.clicked.connect(self.run_right)
         run_all_button.raise_()
 
@@ -132,10 +134,26 @@ def has_output(self) -> bool:
                 return True
         return False
 
+    def _interrupt_execution(self):
+        """ Interrupt an execution, reset the blocks in the queue """
+        for block, _ in self.source_editor.kernel.execution_queue:
+            # Reset the blocks that have not been run
+            block.reset_buttons()
+            block.has_been_run = False
+        # Clear the queue
+        self.source_editor.kernel.execution_queue = []
+        # Interrupt the kernel
+        self.source_editor.kernel.kernel_manager.interrupt_kernel()
+
     def run_left(self, in_right_button=False):
         """
         Run all of the block's dependencies and then run the block
         """
+        # If the user presses left run when running, cancel the execution
+        if self.run_button.text() == "..." and not in_right_button:
+            self._interrupt_execution()
+            return
+
         # If no dependencies
         if not self.has_input():
             return self.run_code()
@@ -164,6 +182,11 @@ def run_left(self, in_right_button=False):
 
     def run_right(self):
         """Run all of the output blocks and all their dependencies"""
+        # If the user presses right run when running, cancel the execution
+        if self.run_all_button.text() == "...":
+            self._interrupt_execution()
+            return
+
         # If no output, run left
         if not self.has_output():
             return self.run_left(in_right_button=True)
@@ -171,10 +194,15 @@ def run_right(self):
         # Same as run_left but instead of running the blocks, we'll use run_left
         graph = self.scene().create_graph()
         edges = bfs_edges(graph, self)
-        blocks_to_run: List["OCBCodeBlock"] = [self] + [v for _, v in edges]
+        blocks_to_run: List["OCBCodeBlock"] = [
+            self] + [v for _, v in edges]
         for block in blocks_to_run[::-1]:
             block.run_left(in_right_button=True)
 
+    def reset_has_been_run(self):
+        """ Reset has_been_run, is called when the output is an error """
+        self.has_been_run = False
+
     def update_title(self):
         """Change the geometry of the title widget"""
         self.title_widget.setGeometry(
diff --git a/opencodeblocks/graphics/kernel.py b/opencodeblocks/graphics/kernel.py
index 7563d9fa..a4c4fcfe 100644
--- a/opencodeblocks/graphics/kernel.py
+++ b/opencodeblocks/graphics/kernel.py
@@ -43,7 +43,7 @@ def message_to_output(self, message: dict) -> Tuple[str, str]:
             # output a print (print("Hello World"))
             out = message['text']
         elif 'traceback' in message:
-            message_type = 'text'
+            message_type = 'error'
             # output an error
             out = '\n'.join(message['traceback'])
         else:
@@ -65,6 +65,7 @@ def run_block(self, block, code: str):
         worker.signals.image.connect(block.handle_image)
         worker.signals.finished.connect(self.run_queue)
         worker.signals.finished_block.connect(block.reset_buttons)
+        worker.signals.error.connect(block.reset_has_been_run)
         block.source_editor.threadpool.start(worker)
 
     def run_queue(self):
diff --git a/opencodeblocks/graphics/worker.py b/opencodeblocks/graphics/worker.py
index 93a3b5d2..abb6185a 100644
--- a/opencodeblocks/graphics/worker.py
+++ b/opencodeblocks/graphics/worker.py
@@ -13,6 +13,7 @@ class WorkerSignals(QObject):
     image = pyqtSignal(str)
     finished = pyqtSignal()
     finished_block = pyqtSignal()
+    error = pyqtSignal()
 
 
 class Worker(QRunnable):
@@ -40,6 +41,8 @@ async def run_code(self):
                     self.signals.stdout.emit(output)
                 elif output_type == 'image':
                     self.signals.image.emit(output)
+                elif output_type == 'error':
+                    self.signals.error.emit()
         self.signals.finished.emit()
         self.signals.finished_block.emit()