Print post title with markup

Using your example, you could…

<h4><?php echo get_the_title( $post_id ); ?></h4>

Or

$h4 = get_the_title();
echo '<h4>' . $h4 . '</h4>';

More on get_the_title().

Or you could use the_title().

the_title( '<h4>', '</h4>' );