Your heuchera plant has rust disease a fungal infection spread by spores and encouraged by poor air circulation. The good news is that this disease seems to be limited to heuchera plants only so it will not spread to other plants. The best treatment is to remove every older and infected leaf so the now bare looking heuchera plant can start fresh and the new growth will not be infected by any old bumpy leaves. Keep rotting plant material away from your heucheras as this may harbor the rust spores. Well rotted compost is okay. Do not fertilizer your heuchera plants with high nitrogen plant foods as this causes soft new growth that is easier for the rust spores to penetrate. You can spray the plants with a fungicide such as Scott Fungus Clear Ultra to help prevent reinfestations. Give your plants plenty of room and do not crowd them. Try to keep the foliage dry. When you pull off all the old and infected leaves do not compost the infected material. Some varieties of heucheras get rust more easily than others. It is sometimes necessary to just stop growing the pale yellow or green heucheras if you find that the darker leaf heucheras are more resistant to rust in your area.  Keep growing, Marianne Binetti