Choking is interference with breathing caused by foreign material in, or compression on, the trachea (windpipe). Thankfully, true choking is a very rare occurrence. Many pet owners will seek veterinary care because they believe their pet has something stuck in its throat, and this is rarely the case. It is far more likely that your pet has something mild and infectious such as tracheobronchitis (commonly called kennel cough) and is coughing or gagging rather than choking.
Frequently, coughing is confused with choking. Both cause the pet to forcefully exhale. With choking, the pet has difficulty inhaling. When coughing, the pet can inhale almost normally. Be careful to distinguish the two: attempting to give first aid to a pet who is merely coughing can cause injury.
If you are in any doubt, have your pet evaluated by a veterinarian. To properly evaluate the throat, pets will require sedation and some will require evaluation with a fiber-optic endoscope or X-rays to look for foreign material. Note, however, that the throat normally contains small bones (the larynx, or voicebox), and since this area is rarely X-rayed, it may be difficult to determine if something abnormal is present.
If the Pet is Unconscious
Perform a Finger Sweep
Open your pet's mouth and do a finger sweep by placing your finger along the inside of the mouth, sliding it down toward the center of the throat over the base of the tongue, and gently "sweeping" toward the center to remove any foreign material. Warning: there is a structure deep in the throat (Adam's apple) that feels like a smooth bone. Do not attempt to pull it out!
Begin Rescue Breathing
Rescue breathing is described in the article on CPR. If air is not entering the lungs, slap the chest wall firmly or perform the Heimlich maneuver by putting the pet on their back, placing your hands over the abdomen near the bottom of the rib cage, and gently but firmly thrusting toward the spine. Perform a finger sweep and begin rescue breathing. Repeat until the foreign body is clear and the lungs can be inflated. Transport to the veterinarian right away.
If the Pet is Conscious
Perform a finger sweep only if it will not excite the pet. Do not perform a finger sweep if you believe your pet will bite you. Stay calm and try to keep the pet calm. If the pet is overheated, cool them with cold water applied to their extremities (ears and feet) and belly, and transport them to the nearest veterinarian or veterinary emergency clinic if there is one in your area. Running the air conditioning in the car on the way may help keep them cool.