Heucheras are remarkably pest and disease free but there is one disease has recently appeared that can be a bit of a problem. Heuchera rust is easily overlooked, it tends to appear on the older leaves and might be mistaken for tatty leaves that have done a whole year and are getting rather tired.....but once you turn a leaf over you'll see the tell-tale pustules and they are hard to confuse with any other Heuchera affliction.
Heucheras have their own special type of rust called Puccinia heucherae, it won't spread to other plants in your garden.
The image below is of both surfaces of leaves from a plant of H 'Lime Rickey' it's a yellow foliage type. The upper surface (left) shows the distinctive pock marks and the lower surface shows the little pockets of spores which eventually burst and scatter themselves on the wind.
Because the spores develop within the leaf tissue the spore clusters can't be picked off like a gall or scale insect. Take a look with a hand lens and you'll see the transparent covering of the outer layer of leaf tissue.
It's worth trying to keep rust under control because it spoils the appearance of the leaves and weakens the plant.
The first thing to do is cut off the leaves of the affected plant, all of them but don't remove the growing points of the plant. Heucheras grow back very quickly and when it comes the new foliage should be fresh, rust free and lovely. Dispose of the leaves so as to avoid spreading the spores - burning is a good idea or pop them in the rubbish bin (not with the green waste).
You can spray with Systhane (Roseclear) or Fungus Fighter to prevent further development of the disease. Always follow the instructions on the product label.