Secrets of the Heart was published by Signet in April 1988 and was one of their "Super Regencies". They started publishing longer stories under this line. This cover was a reprint of an earlier version and with a tiny picture by Allan Kass. I'm pretty sure that it's an original painting and not a cover done for another book. Of course, it's small and shows a head shot of our couple. ** Edit** I realized that this cover's headshot is the same as the illustration for Norma Lee Clark's Cupid's Calendar! Recycling at its best!
Secrets of the Heart is a story of love lost and then found. Sarah is married to the Duke of Cranwell, but their love is tested after their marriage by her secret past. It looks as if their marriage ends before it really begins, but later, in Bath, they meet again and wonder if they should pursue a formal separation and divorce, when cupid strikes our pair again!
Some of Signet's most popular authors wrote for the Super Regency line: Edith Layton, Barbara Allister, and Mary Balogh are the few that come to mind. I believe that this was the beginning of the regency historical romance. Authors were able to pen a longer story line and add some plots that they couldn't in the shorter regencies. Nowadays, thin regencies are only published by Harlequin, but many authors who began in the regency genre are writing books set in regency times in the thicker historical romances.