Loop – first header tag

I only want the first header tag in the following code to be H1 and the following tags to be H2, I used to know how to do this, but I’ve complete forgotten. Can anyone point me in the right direction?

Thank you

<?php
	$args = array( 'post_type' => 'discussion', 'posts_per_page' => 1 );
$loop = new WP_Query( $args );
while ( $loop->have_posts() ) : $loop->the_post();
  echo '<div class="headline-discussion">';
  ?>

   <?php echo '<div class="headdisc-image">';

if ( has_post_thumbnail() ) { // check if the post has a Post Thumbnail assigned to it.
	the_post_thumbnail();
}
  echo '</div>';

  ?>

     <div class="post">

				<h1 class="toptitle"><a href="<?php the_permalink() ?>"><?php the_title(); ?></a></h1>

			<div class="entry">
				<?php the_excerpt(); ?>
			</div>
		</div>

  </div>
  <?php
endwhile; ?>