Bloat is a medical condition in which the stomach becomes overstretched by excessive gas content. It is also commonly referred to as torsion, gastric torsion, and gastric dilatation-volvulus (GDV) when the stomach is also twisted.... The condition occurs most commonly in domesticated animals, especially ruminants and certain dog breeds.

In dogs, gas accumulation in the stomach is usually associated with volvulus of the stomach, which prevents gas from escaping. Deep-chested breeds are especially at risk. Mortality rates in dogs range from 10 to 60 percent, even with treatment. With surgery, the mortality rate is 15 to 33 percent....

Symptoms:
Symptoms are not necessarily distinguishable from other kinds of distress. A dog might stand uncomfortably and seem to be in extreme discomfort for no apparent reason. Other possible symptoms include firm distension of the abdomen, weakness, depression, difficulty breathing, hypersalivation, and retching without vomiting. A high rate of dogs with bloat have cardiac arrhythmias (40 percent in one study). Chronic bloat may occur in dogs, symptoms of which include loss of appetite, vomiting and weight loss.

Treatment:
Bloat is an emergency medical condition: having the animal examined by a veterinarian is imperative. Bloat can become fatal within a matter of minutes.

Source: http://en.wikipedia.org/wiki/Bloat