The tongue in Traditional Chinese medicine is the mirror of the heart. The appearance of the tongue indicates the healthiness and physical strength of your body.
Your practitioner will be looking at the overall tongue; colour, pale, red, cracks, etc, the size; short, long, fat, thin etc., the coating; yellow, thick, thin, no coating, white etc. The health of your body reflects on your tongue. Have you ever noticed the changes occurring on your tongue when you've had the flu, been constipated, or had a stroke?
One can see the progression of a diseased state in the body and your practitioner will support the next organs. As an illness progresses a chain of events can occur which may affect one organ first and others may follow. This is the preventative side of Traditional Chinese medicine.
With this in mind combined with the pulse diagnosis and other manifestations a TCM diagnosis is formed and a treatment protocol is followed.