Cardiopulmonary Resuscitation (CPR and Rescue Breathing)
CPR is the method used to treat an animal who is not breathing or has no heartbeat (check for unresponsiveness). It consists of rescue breathing (also called mouth to nose/mouth resuscitation) and chest compressions. CPR is based on three basic principles, called the ABCs of CPR.
You must follow the ABC order (Airway, Breathing, Circulation) when attempting CPR. 
Even when performed by an experienced veterinarian, CPR does not always work. Don't be discouraged if your attempt fails, but know that you did try to save an animal's life.
*
Does the animal have an open airway? (The airway is the passage the animal breathes through. Check to see if the throat and mouth are clear of foreign objects.) If the answer is
YES, go to Breathing. If the answer is
NO, you need to open the airway. Do the following:
1. Lay the animal down, on either side.
2. Gently tilt the head slightly back to extend the neck and head.
3. Pull the tongue between the front teeth.
4. Use your finger to check for and remove any foreign material or vomit from the mouth.
Do not place your fingers inside the mouth of a conscious animal--you may be bitten! B=Breathing
* Is the animal breathing (check chest rise and fall, or place a soft/light object by nose to see if it moves)? If the answer is
YES, allow the animal to assume the body position most comfortable for them. Then, move on to Circulation. If the answer is
NO, do the following:
1. Make sure the airway is open (see
Airway above).
2. Seal the mouth and lips by placing your hands around the lips, gently holding the muzzle closed.
3. Place your mouth over the animal's nose and forcefully exhale. Watch for chest rise and fall. This is how you will know if the airway is clear and air is flowing into the lungs. If the airway is NOT clear, the chest will not rise. If this happens, reposition the head and re-check the airway.
4. If you find a patent airway, give four or five breaths rapidly, then check to see if your pet is breathing without assistance (watch chest rise). If the animal begins to breath, but the breathing is shallow and irregular, or if breathing dos not begin, continue artificial respiration until you reach the veterinary hospital or for a maximum of 20 minutes. (Beyond 20 minutes there is little chance of reviving your pet.)
Do not attempt this on a conscious animal.
Use the following breathing rates:
* Small dog (under 30 pounds) or cat: 20-30 breaths per minute.
C=Circulation
* Is there a heartbeat or a pulse (check pulse on the inner leg by the groin)? If the answer is
NO, perform chest compressions (on a hard surface, not a bed). Do the following:
Small Dog (under 30 Pounds) or Cat
1. Lay your pet down, on the animal's
right side.
2. Kneel next to your pet with the animal's chest facing you.
3. Place the palm of one of your hands over the ribs at the point where the elbow touches the chest. Place your other hand underneath the right side of the animal.
4. Compress the chest 1/2-1 inch (your elbows should be softly locked during compressions).
5. Chest compressions are alternated with breaths.
6. If working alone, do five compressions for each breath, then check for a pulse.
7. If there are two people, one person does the breathing while the other does the compressions at a rate of three compressions for each breath, then check for a pulse.
Do not assume there is no heartbeat or pulse simply because an animal is not breathing. Do not start chest compressions before checking for a heartbeat. (If the animal is conscious and responds to you, then the heart is beating).
Continue CPR until the animal has a strong heartbeat and pulse, or until you reach the veterinary hospital, or until 20 minutes have passed and your efforts have not been successful.
CPR can be performed on the way to the veterinary hospital, as long as there are at least two people present (one to drive).
American Red Cross Pet Fist Aid, Bobbie Mammato, DVM, MPH, 1997, pp. 15-17. Most of the above was taken word for word. There are times where I added a little extra explanation. Also, please see short slide show below.
[CPR info compiled by BabyFidgette]