What heading to use in a Bootstrap alert

In Bootstrap there are dedicated alerts. https://v4-alpha.getbootstrap.com/components/alerts/

According to the code on that site, the headings in an alert shall be h4, but I'm not quite sure that's the correct heading level.

• If I use h1, there will be two h1 headings on the same page.
• If i use h2, there will be a h2 before the h1 on that page.
• If I avoid using headers, users with screen readers (just braille, no speach) might miss the information when browsing that page.

Are there any other options except of those above, or are any of these options the correct way to handle this issue?