What does it mean to be declared dead?
When someone is declared dead, it is not solely because their heart has stopped beating; the official distinction (in a legal or medical capacity) between life and death also depends on the absence or irreversible lack of brain activity. This allows for two possibilities: cardiopulmonary failure and irreversible cessation of all brain functions.
Cardiopulmonary failure, as the name suggests, is the complete cessation of lung and heart activity within the body. The heart is the instrument that provides blood to the rest of the body. The lungs, which comprise the “pulmonary” aspect of the word, are responsible, in a more simplified context, for the exchange of gases in venous blood, replacing carbon dioxide in blood with oxygen.
Loss of function in the brain, specifically when it is irreversible, is another constituent of the declaration of death. This criterion, arguably the more interesting of the two, occurs when the the whole brain, including the hindbrain, midbrain, and forebrain, ceases to function.
The brain has many different methods of classification, and this paper follows the hindbrain/midbrain/forebrain system. This system compartmentalizes regions of the brain by overall function. Researchers and evolutionary biologists find hindbrains in nearly all organisms, as this is the portion of the brain that is responsible for vital bodily functions, such as breathing and heartbeat.
The midbrain and the forebrain are responsible for more complex cognitive processes, such as emotion and long-term memory storage. The highly developed facets of function and parts that humans possess are what allow for executive processing, multi-step thinking, and complex problem-solving.
Death by organ failure is also another viable possibility, although it is as an offshoot of the two aforementioned methods. For example, a palliative patient with liver failure does not die as a result of the liver itself failing, but as a result of the implications an organ failure can cause. The liver, responsible for detoxifying the blood, closely interacts with the circulatory and digestive systems. With toxins still present in the blood, liver failure makes a person much more susceptible to systemic infections, such as sepsis. Additionally, the blood is a vital component of the body because of its rapid transportation. Without acceptable blood chemistry, toxins accumulate in other organs, setting off an organ failure cascade.
Undoubtedly, toxins reach the brain and the heart, our organs of interest. The toxin buildup causes these organs to finally shut down as well. Systemic organ failure is incredibly difficult to treat, as communication between regions of the body generally occurs far more rapidly than potential intervention can reach. This is why infections of the bloodstream, such as sepsis, are so deadly.
With this in mind, some may wonder whether artificial stimulation of the brain or heart equates to life. Modern medicine distinguishes between maintaining organ function and maintaining biological life. Therefore, someone who requires mechanical ventilation can be classified as alive if brain function persists. However, if the entire brain, including the brainstem, has irreversibly ceased functioning, the person is declared medically and legally deceased.
Although every organ contributes to survival, the brain and circulatory-respiratory systems hold particular significance because they determine whether the body can maintain itself as an integrated organism.
References
Cleveland Clinic. (2024). Brain Death: What It Is, Stages & Criteria. Cleveland Clinic. https://my.clevelandclinic.org/health/diseases/brain-death
Eid, D. (2021, April 19). Forebrain, Midbrain and Hindbrain | Simply Psychology. Www.Simplypsychology.Org. https://www.simplypsychology.org/forebrain-midbrain-hindbrain.html
End-stage Liver Disease (ESLD) | UCSF Department of Surgery. (n.d.). Surgery.Ucsf.Edu. Retrieved July 10, 2026, from https://surgery.ucsf.edu/condition/end-stage-liver-disease-esld
Mayo Clinic. (2025). Heart failure. Mayo Clinic. https://www.mayoclinic.org/diseases-conditions/heart-failure/symptoms-causes/syc-20373142