Bloat is the common term for Gastric Dilation-Torsion Complex.  This condition involves swelling of the stomach from gas, fluid or both.  As the stomach swells, it may rotate 90° to 360°, twisting between its fixed attachments at the esophagus (food tube) and at the duodenum (the upper intestine). 

The twisting stomach traps air, food, and water in the stomach.  The bloated stomach obstructs veins in the abdomen, leading to low blood pressure, shock, and damage to internal organs.  The combined effect can quickly kill a dog. 

Bloat is a life-threatening veterinary emergency and can kill in less than an hour  

SYMPTOMS OF BLOAT:  If you see ANY combination of these symptoms and suspect bloat, get the dog to your veterinarian or an emergency clinic as quickly as possible.  Do not wait until you feel/see an enlarged stomach! Once the stomach has twisted (torsion) no first aid can cure bloat and emergency veterinary intervention is the only option

• Attempts to vomit (usually unsuccessful); may occur every 5-20 minutes

•     Continuous pacing or lying down in odd places

•     Anxiety / restlessness / inability to get comfortable

•      "Hunched up" or "roached up" appearance

•      Excessive drooling, usually accompanied by retching noises

•       Bloated abdomen that may feel tight (like a drum)
  Despite the term "bloat," often this symptom never occurs or is not apparent

•       Pale, off-color or cold gums

•      Lack of normal gurgling and digestive sounds in the tummy

•     Coughing or unproductive gagging

•       Foamy mucous around the lips, or vomiting foamy mucous

•      Unproductive attempts to defecate

•      Licking the air

•       Seeking a hiding place

•       Looking at their side or other evidence of abdominal pain or discomfort

•       Refusing to lie down or sit down

•      Spread-legged stance (especially in advanced stage)

•       May attempt to eat small stones and twigs

•      Drinking excessively

•      Heavy or rapid panting, shallow breathing

•      Accelerated heartbeat (heart rate increases as bloating progresses)

•       Weak pulse

•       Collapse

The following links provide more information on bloat, its prevention and first aid.

About Bloat

Bloat FAQ

Canis Major On Bloat

Devine Farm Mastiff Bloat Information

Canine Bloat

A Breeder's Comments On The Purdue Bloat Study

TIPS FOR PREVENTING BLOAT

•  Feed several smaller meals rather than one large meal a day to reduce the bulk in the GI tract
   http://www.jaaha.org/cgi/content/abstract/40/3/192

• Feed in bowl on ground rather than an elevated container. 
        (This is recent change from a common recommendation that dogs be fed from an elevated   container, and is based on the belief that food that is fed from a lower position will spend more time being pre-digested by digestive enzymes in the dog’s mouth and by the chewing process, reducing the stomach’s digestive “load” and subsequent gaseous by-products.  Still, personal opinion and study results continue to vary regarding ground-level vs.elevated feeding.)
   

• Avoid dry foods that list oils or fats among the first four label ingredients when feeding dogs with a previous occurrence or family history of bloat. 
        http://www.jaaha.org/cgi/content/abstract/42/1/28

• Do not feed when the dog is stressed, over-heated or immediately following strenuous exercise.  Immediately after a meal, the dog should have be allowed to rest comfortably and not be allowed to exercise strenuously or be put into a stressful situation.

• Do not allow your dog to drink too much water immediately before or after a meal.  Other than immediately before and after meals, dogs should have access to clean water at all times.

• When switching dog foods, do so gradually (allow several weeks).

• Always keep a product with simethicone (e.g., Mylanta Gas [not regular Mylanta], Mylicon Drops, Phazyme, Gas-X, etc.) on hand to treat gas symptoms.  Liquid simethicone is available over-the-counter for infants or can be obtained by piercing the end of a liquid-filled simethicone capsule with a pin. 

Note: 

If torsion (twisting) has already occurred, simethicone will not be able to reach the stomach and will not relieve bloat. 

Some recommend giving simethicone immediately if the dog burps more than once or shows other signs of gas.

Others report relief of gas symptoms with 1/2 tsp of nutmeg or the homeopathic remedy Nux moschata 30
 

    Many owners of breeds that are prone to bloat have veterinarians “tack” the stomach into place while performing other abdominal surgeries to prevent the deadly torsion (twisting) in the event the dog bloats in the future.