Heath and heather only, just as they grow in their natural habitats. Besides, the shrubs will shade them; soil requirements for both will probably not be met; and visually, such plantings would beg the question, "why?," rather than a response of "ahhh!"

Depends on what kinds of shrubs and how close together you wish to plant them.

Heathers mix beautifully with conifers.

Heathers also will mix with dwarf rhododendrons or other small shrubs that have similar cultural requirements.

Old thread but I will say that in my experience, the central and southern european heaths (Erica X griffithsii, Erica terminalis, etc.) have an especially dislike of crowding and being shaded out by other plants.
Erica carnea would probably be ok between shrubs if it were a southern exposure and they still got plenty of sun.

Duh, my bad, Erica carnea is central European. But native to quite high altitudes in alpine areas. I was thinking more of the zn 7-ish species that are larger, shrubier, and native to drier climates.
I did once have an Erica vagans intermingle with some azaleas and it did ok, but it was SE facing so the azaleas weren't shading out the Erica. OTOH I had an Erica terminalis suddenly die because a Salvia shaded it out.

I have heaths and heathers intermingled wit shrubs, grasses, perennials and bulbs all over my yard. As long as they aren't flopped on or shaded out, they do fine.

I'VE HAD GOOD LUCK WITH MIXED PLANTINGS OF SHRUBS, DWARF CONIFERS, PHORMIUMS, GRASSES, SUCCULENTS AND HEATHERS. HAPPY TO SEND PHOTOS TO ANYONE WHO WANTS THEM. THE GARDEN WAS FEATURED IN APRIL 08 ISSUE OF GARDENS WEST MAGAZINE SO YOU CAN SEE IT THERE TOO. GOOD LUCK!

They go great with Rhododendrons and Pieries, but give each plenty of space when planting. I have cold weather varieties and they do spread to a good 3-4 feet wide over time. One is HUGE in full sun, the other is half the size in partial shade from an Oak tree (15 year old plants).