How to insert a (line)break after (each) <h3> element?

How to insert a (line)break after (each) <h3> element?

Lets start with a sample code:

  1. <h3>title line</h3>
  2. <figure .....>
  3. <img ....>....</img>
  4. <div>...</div>
  5. </figure>
  6. <div>...</div>

When I print a webpage into a pdf file then it happens occasionally that the image is visually appended right of the h3 headline. I don't want this.
Such an image should ALWAYS be placed immediately BELOW a <h3> headline.
So I would like to insert (from a jQuery script) something like a hard line break after each <h3>....</h3> element.

How can I achieve this?

A <br/>  seems not sufficient.