The most common cause of deep pain on the bottom surface of the heel is plantar fasciitis (inflammation of the plantar fascia). The plantar fascia is a broad band of fibrous tissue which runs along the bottom surface of the foot, from the heel to the toes. Long standing inflammation causes an inflammation at the point where the fascia inserts into the heel bone. These results in the appearance of a bony heel spur on x-ray. The spur itself is not the source of the pain. 
Causes
- Excessive load on the foot from obesity or overuse
- Excessive flattening of the arch on weight bearing
- Tight plantar fascia, common in persons with high arched feet
- Over pronation of the foot (a complex motion including outward rotation of the heel and inward rotation of the ankle).
What you can do
- Application of ice to the heel area after prolonged activity
- Wear supportive shoes with a stiff heel counter (the part of the shoe which wraps around the heel) and a good arch. A well made running or walking shoe is a good example.
- Sometimes a shoe with a moderately high heel will relieve pressure on the fascia
- Stretching and strengthening exercises will stretch the plantar fascia and strengthen the small intrinsic muscles which stabilize the arch. This should not be attempted when the heel is sore.
- Over-the-counter anti-inflammatory medications containing ibuprofen or aspirin, when tolerated
What the doctor may do
- Prescription doses of anti-inflammatory medication
- Inject powerful anti-inflammatory medication to calm inflammation around the painful area
- Apply taping to relieve strain on the plantar fascia
- Administer physical therapy (e.g. ultrasound, cold laser)
- Control foot function with an orthotic (insole)
- Prescribe special splints to help stretch the fascia
- Surgical release of the plantar fascia and excision of the heel spur (rarely required).
