Create new page.
(Note: Do not click on Use The Divi Builder button.)
In the Page Attributes section, under Template, choose IFrame
In the main text box (the one under the “use the divi builder” button), click the Text tab (top right of this box)
Enter the URL of the page (eg. https://mplsheart.org) here.
Your page (URL) will appear in the iframe now.