A heel spur is a calcium deposit that sticks out from the back of your heel that can cause large amounts of pain and irritation. These buildups usually arise over the course of many months and are the product of strains on the muscles and ligaments in the foot.  Plantar fasciitis is also a common factor associated with the formation of heel spurs. The plantar fascia is a fibrous band of connective tissue that connects the heel bone to the ball of your foot, and when this becomes inflamed it is known as plantar fasciitis.