Cardiopulmonary arrest (CPA) occurs when normal blood circulation ceases due to the heart’s inability to contract (heart failure). Like many other body systems, the respiratory and cardiovascular systems work in a coordinated fashion. Cardiac arrest can occur in dogs and cats of any age, sex, or breed. Cardiac arrest can occur due to many circumstances. From end-stage disease, to arrhythmias, to different types of cancer, cardiopulmonary arrest is an unfortunate complication of many injuries and illnesses. 
When a cardiopulmonary arrest occurs in your practice, having a well- trained team ready to provide high-quality CPR may be the difference between life and death for your patient. The importance of team training for CPA response is a big part of the Recover Clinical Guidelines, produced by the Journal of Veterinary Emergency and Critical Care, which recommends
refresher training at least every six months. The success of cardiopulmonary resuscitation (CPR) efforts depends on many factors, including the underlying cause of the arrest, the timeliness and effectiveness of the intervention, and the preparedness of the team administering CPR.
Overall prognosis of recovery from cardiopulmonary arrest (CPA) with CPR efforts is as high as 35%–44%; however, only <10% of animals survive to discharge. A few years ago, over 100 board certified veterinary specialists from around the world collaborated to develop the Reassessment Campaign on Veterinary Resuscitation (RECOVER) evidence-based veterinary CPR guidelines. Prior to the publication of the new advance in CPA management, the absence of standardized guidelines or training for cardiopulmonary resuscitation (CPR) in veterinary medicine has been cited as a major factor in the historically poor outcomes for dogs and cats in cardiac arrest. However now that we have a set of industry standards for managing cardiopulmonary arrest, we have found that when CPR is done correctly, 50% of dogs and cats that arrest in the peri- anesthetic period survive to discharge. To have a full understanding of Basic as well as Advanced Life Support in dogs and cats, it is first important to understand the function and subsequent dysfunction in CPA, of the cardiac as well as respiratory systems. 
The Heart is a muscular organ about the size of a fist that pumps blood through the network of arteries and veins called the cardiovascular system. The heart pumps blood with a rhythm determined by a group of pace-making cells in the sinoatrial node. These cells generate a current that causes contraction of the heart, traveling through the conduction system of the heart. The heart receives blood low in oxygen from the systemic circulation. From here it is pumped through the lungs where it receives oxygen and gives off carbon dioxide. Oxygenated blood then returns to the heart and is pumped out to the body.
The heart has four chambers:
Electrical Conduction is the electrical impulse that travels from the sinus node to the atrioventricular node (also called AV node). There, impulses are slowed down for a very short period, then continue down the conduction pathway via the bundle of His into the ventricles. The bundle of His divides into right and left pathways, called bundle branches, to stimulate the right and left ventricles. Cardiac Output is the result of the stroke volume and the heart rate. Stroke volume is the amount of blood pumped during each contraction of the ventricle and the heart rate is the number of times the ventricle contracts per minute. A normal dog’s cardiac output is 100mL/kg/min and a normal stroke volume is 1-2 mL/kg. To increase cardiac output (goal in CPR) you can either increase stroke volume, increase heart rate or increase both stroke volume and heart rate.
Three primary dysfunctions of the heart are Asystole, Pulseless Electrical Activity (PEA) and Ventricular Fibrillation.