diff --git a/mailpoet/lib/EmailEditor/Engine/SettingsController.php b/mailpoet/lib/EmailEditor/Engine/SettingsController.php
index 01d847a2d7..a92b713595 100644
--- a/mailpoet/lib/EmailEditor/Engine/SettingsController.php
+++ b/mailpoet/lib/EmailEditor/Engine/SettingsController.php
@@ -70,6 +70,8 @@ class SettingsController {
       ['css' => $flexEmailLayoutStyles],
     ];
 
+    $settings['styles'] = apply_filters('mailpoet_email_editor_editor_styles', $settings['styles']);
+
     $settings['__experimentalFeatures'] = $themeSettings;
     // Enable border radius, color, style and width where possible
     $settings['__experimentalFeatures']['border'] = [
diff --git a/mailpoet/lib/EmailEditor/Integrations/Core/Initializer.php b/mailpoet/lib/EmailEditor/Integrations/Core/Initializer.php
index e773d78446..2a7d929b0b 100644
--- a/mailpoet/lib/EmailEditor/Integrations/Core/Initializer.php
+++ b/mailpoet/lib/EmailEditor/Integrations/Core/Initializer.php
@@ -9,6 +9,8 @@ class Initializer {
   public function initialize(): void {
     add_action('mailpoet_blocks_renderer_initialized', [$this, 'registerCoreBlocksRenderers'], 10, 1);
     add_filter('mailpoet_email_editor_theme_json', [$this, 'adjustThemeJson'], 10, 1);
+    add_filter('mailpoet_email_editor_editor_styles', [$this, 'addEditorStyles'], 10, 1);
+    add_filter('mailpoet_email_renderer_styles', [$this, 'addRendererStyles'], 10, 1);
   }
 
   /**
@@ -35,4 +37,16 @@ class Initializer {
     $editorThemeJson->merge(new \WP_Theme_JSON($themeJson, 'default'));
     return $editorThemeJson;
   }
+
+  public function addEditorStyles(array $styles) {
+    $declaration = (string)file_get_contents(dirname(__FILE__) . '/styles.css');
+    $styles[] = ['css' => $declaration];
+    return $styles;
+  }
+
+  public function addRendererStyles(string $styles) {
+    $declaration = (string)file_get_contents(dirname(__FILE__) . '/styles.css');
+    $styles .= $declaration;
+    return $styles;
+  }
 }
diff --git a/mailpoet/lib/EmailEditor/Integrations/Core/Renderer/Blocks/Heading.php b/mailpoet/lib/EmailEditor/Integrations/Core/Renderer/Blocks/Heading.php
index 6f4b146545..7e453867ae 100644
--- a/mailpoet/lib/EmailEditor/Integrations/Core/Renderer/Blocks/Heading.php
+++ b/mailpoet/lib/EmailEditor/Integrations/Core/Renderer/Blocks/Heading.php
@@ -9,7 +9,7 @@ use MailPoet\Util\Helpers;
 class Heading implements BlockRenderer {
   public function render(string $blockContent, array $parsedBlock, SettingsController $settingsController): string {
     $level = $parsedBlock['attrs']['level'] ?? 2; // default level is 2
-    $blockContent = $this->removePaddingFromElement($blockContent, ['tag_name' => "h{$level}"]);
+    $blockContent = $this->adjustStyleAttribute($blockContent, $parsedBlock, $settingsController, ['tag_name' => "h{$level}"]);
     return str_replace('{heading_content}', $blockContent, $this->getBlockWrapper($parsedBlock, $settingsController));
   }
 
@@ -17,7 +17,7 @@ class Heading implements BlockRenderer {
    * Based on MJML <mj-text>
    */
   private function getBlockWrapper(array $parsedBlock, SettingsController $settingsController): string {
-    $themeData = $settingsController->getTheme()->get_data();
+
     $availableStylesheets = $settingsController->getAvailableStylesheets();
 
     // Styles for padding need to be set on the wrapping table cell due to support in Outlook
@@ -39,10 +39,6 @@ class Heading implements BlockRenderer {
       $styles[$property] = $value;
     }
 
-    if (!isset($styles['font-size'])) {
-      $styles['font-size'] = $themeData['styles']['typography']['fontSize'];
-    }
-
     $styles = array_merge($styles, $this->fetchStylesFromBlockAttrs($availableStylesheets, $parsedBlock['attrs']));
 
     return '
@@ -113,13 +109,21 @@ class Heading implements BlockRenderer {
   }
 
   /**
+   * 1) We need to remove padding because we render padding on wrapping table cell
+   * 2) We also need to replace font-size to avoid clamp() because clamp() is not supported in many email clients.
+   * The font size values is automatically converted to clamp() when WP site theme is configured to use fluid layouts.
+   * Currently (WP 6.4), there is no way to disable this behavior.
    * @param array{tag_name: string, class_name?: string} $tag
    */
-  private function removePaddingFromElement($blockContent, array $tag): string {
+  private function adjustStyleAttribute($blockContent, array $parsedBlock, SettingsController $settingsController, array $tag): string {
     $html = new \WP_HTML_Tag_Processor($blockContent);
+    $themeData = $settingsController->getTheme()->get_data();
+    $fontSize = 'font-size:' . ($parsedBlock['email_attrs']['font-size'] ?? $themeData['styles']['typography']['fontSize']) . ';';
+
     if ($html->next_tag($tag)) {
       $elementStyle = $html->get_attribute('style') ?? '';
       $elementStyle = preg_replace('/padding.*:.?[0-9]+px;?/', '', $elementStyle);
+      $elementStyle = preg_replace('/font-size:[^;]+;?/', $fontSize, $elementStyle);
       $html->set_attribute('style', $elementStyle);
       $blockContent = $html->get_updated_html();
     }
diff --git a/mailpoet/lib/EmailEditor/Integrations/Core/styles.css b/mailpoet/lib/EmailEditor/Integrations/Core/styles.css
new file mode 100644
index 0000000000..26ae5a28ef
--- /dev/null
+++ b/mailpoet/lib/EmailEditor/Integrations/Core/styles.css
@@ -0,0 +1,23 @@
+h1 {
+  font-size: 48px;
+}
+
+h2 {
+  font-size: 42px;
+}
+
+h3 {
+  font-size: 36px;
+}
+
+h4 {
+  font-size: 26px;
+}
+
+h5 {
+  font-size: 20px;
+}
+
+h6 {
+  font-size: 13px;
+}
diff --git a/mailpoet/tests/integration/EmailEditor/Integration/Core/Renderer/Blocks/HeadingTest.php b/mailpoet/tests/integration/EmailEditor/Integration/Core/Renderer/Blocks/HeadingTest.php
index 4e79ebe1d4..55ecde9c23 100644
--- a/mailpoet/tests/integration/EmailEditor/Integration/Core/Renderer/Blocks/HeadingTest.php
+++ b/mailpoet/tests/integration/EmailEditor/Integration/Core/Renderer/Blocks/HeadingTest.php
@@ -20,11 +20,13 @@ class HeadingTest extends \MailPoetTest {
       'style' => [
         'typography' => [
           'textTransform' => 'lowercase',
+          'fontSize' => '24px',
         ],
       ],
     ],
     'email_attrs' => [
       'width' => '640px',
+      'font-size' => '24px',
     ],
     'innerBlocks' => [],
     'innerHTML' => '<h1 class="has-pale-cyan-blue-color has-vivid-red-background-color has-text-color has-background">This is Heading 1</h1>',
@@ -46,6 +48,7 @@ class HeadingTest extends \MailPoetTest {
     $rendered = $this->headingRenderer->render('<h1>This is Heading 1</h1>', $this->parsedHeading, $this->settingsController);
     verify($rendered)->stringContainsString('This is Heading 1');
     verify($rendered)->stringContainsString('width: 100%;');
+    verify($rendered)->stringContainsString('font-size:24px;');
     verify($rendered)->stringNotContainsString('width:640px;');
   }
 
@@ -56,4 +59,9 @@ class HeadingTest extends \MailPoetTest {
     verify($rendered)->stringContainsString('text-transform:lowercase;');
     verify($rendered)->stringContainsString('text-align:center;');
   }
+
+  public function testItReplacesFluidFontSizeInContent(): void {
+    $rendered = $this->headingRenderer->render('<h1 style="font-size:clamp(10px, 20px, 24px)">This is Heading 1</h1>', $this->parsedHeading, $this->settingsController);
+    verify($rendered)->stringContainsString('font-size:24px');
+  }
 }
diff --git a/mailpoet/tests/integration/EmailEditor/Integration/Core/Renderer/RendererTest.php b/mailpoet/tests/integration/EmailEditor/Integration/Core/Renderer/RendererTest.php
index f7424a0726..38f95c62bb 100644
--- a/mailpoet/tests/integration/EmailEditor/Integration/Core/Renderer/RendererTest.php
+++ b/mailpoet/tests/integration/EmailEditor/Integration/Core/Renderer/RendererTest.php
@@ -22,19 +22,32 @@ class RendererTest extends \MailPoetTest {
       'post_content' => '<!-- wp:button --><div class="wp-block-button"><a class="wp-block-button__link has-background wp-element-button">Button</a></div><!-- /wp:button -->',
     ]);
     $rendered = $this->renderer->render($emailPost, 'Subject', '', 'en');
-    $doc = new \DOMDocument();
-    $doc->loadHTML($rendered['html']);
-    $xpath = new \DOMXPath($doc);
-    $nodes = $xpath->query('//td[contains(@class, "wp-block-button")]');
-    $button = null;
-    if (($nodes instanceof \DOMNodeList) && $nodes->length > 0) {
-      $button = $nodes->item(0);
-    }
-    $this->assertInstanceOf(\DOMElement::class, $button);
-    $this->assertInstanceOf(\DOMDocument::class, $button->ownerDocument);
-    $buttonHtml = $button->ownerDocument->saveHTML($button);
+    $buttonHtml = $this->extractBlockHtml($rendered['html'], 'wp-block-button', 'td');
     verify($buttonHtml)->stringContainsString('color:#ffffff');
     verify($buttonHtml)->stringContainsString('padding:.7em 1.4em');
     verify($buttonHtml)->stringContainsString('background:#32373c');
   }
+
+  public function testItInlinesHeadingFontSize() {
+    $emailPost = new \WP_Post((object)[
+      'post_content' => '<!-- wp:heading {"level":1,"style":{"typography":{"fontSize":"large"}}} --><h1 class="wp-block-heading">Hello</h1><!-- /wp:heading -->',
+    ]);
+    $rendered = $this->renderer->render($emailPost, 'Subject', '', 'en');
+    $headingHtml = $this->extractBlockHtml($rendered['html'], 'wp-block-heading', 'h1');
+    verify($headingHtml)->stringContainsString('font-size:48px'); // large is 48px
+  }
+
+  private function extractBlockHtml(string $html, string $blockClass, string $tag): string {
+    $doc = new \DOMDocument();
+    $doc->loadHTML($html);
+    $xpath = new \DOMXPath($doc);
+    $nodes = $xpath->query('//' . $tag . '[contains(@class, "' . $blockClass . '")]');
+    $block = null;
+    if (($nodes instanceof \DOMNodeList) && $nodes->length > 0) {
+      $block = $nodes->item(0);
+    }
+    $this->assertInstanceOf(\DOMElement::class, $block);
+    $this->assertInstanceOf(\DOMDocument::class, $block->ownerDocument);
+    return (string)$block->ownerDocument->saveHTML($block);
+  }
 }