The sudden death of a beloved pet can be a traumatic event for many pet owners. The American Veterinary Medical Association reports that there has been very little in the veterinary literature about the causes of unexpected death in pets.

One Canadian study done in the early 2000s found that the most common causes of sudden death in dogs were:

• heart disease
• toxicosis (poisoning)
• gastrointestinal disease
• trauma
• hemorrhage not associated with trauma

For cats, the top causes were found to be:

• trauma (outdoor cats)
• heart disease
• intestinal disease
• respiratory disease
• urinary tract disease

A veterinarian who conducted a more recent study (2019) on the causes of sudden death among pets in Ontario, Canada shared her results with the AVMA.

For dogs, the most common causes were:

• underlying occult neoplasia (unknown cancer), mostly hemangiosarcoma (blood vessel lining)
• cardiac disease
• respiratory disease, mostly resulting from aspirated food
• trauma
• gastrointestinal accidents

Among cats, the most common causes were found to be:

• underlying cardiac disease, especially cardiomyopathy
• trauma
• miscellaneous inflammatory conditions
• cases with no detectable lesions or cause of death
• miscellaneous infectious conditions

Intentional poisoning by neighbors or strangers was not found to be a significant cause of sudden death. Postmortem examinations of pets often find a previously unknown underlying health condition. Trauma deaths are most often caused by cars or attacks by other animals.

Veterinarians say that sometimes there are no outward signs of illness in a pet up until the time of death. This can happen with tumors, abnormal heart rhythm, or a blood clot in the lungs.

Performing a necroscopy on a pet that dies suddenly can be a good way to provide closure for owners, and it can also help further understanding of the issue among veterinary health professionals.

One veterinary pathologist told the AVMA, “Our clients are generally very appreciative of knowing the specifics of what happened and being able to talk about it with a professional pathologist. These pets have been beloved members of the family, and the necropsy—and the answers that come with it—seems to really help the grieving process. It helps give them closure.”