While driving back home, the boys get into a car accident, in which Christophe and Johan are only mildly injured while Simon experiences severe bodily trauma and immediately slips into a coma.

At the hospital, Dr. Pierre Révol, the head physician of the intensive care unit (ICU) department, discovers that Simon is unresponsive to auditory, visual, and tactile stimulation, and that his brain has suffered irreversible damage.

Eventually, Dr. Révol declares Simon to be in a state of brain death, in which he can only maintain involuntary cardiac and respiratory functions with the assistance of a ventilator and other machines, and he does not display any cerebral activity.

Sean indignantly accuses Dr. Révol and the rest of the ICU staff for not doing enough to save Simon, while Marianne, along with her husband, grapples with their son's death and blames herself for failing to protect him from his precarious lifestyle.

Throughout the novel, Marianne and Sean struggle with the passing of their son Simon, a strong, healthy young man who lived his life fearlessly and immensely.

Sean, who is the most resistant to donating Simon's organs, expresses his desire to preserve his son's body and is repulsed by the idea of it being cut up and destroyed during the operation.

To the Limbres, Simon's body is not merely a large mass of skin, tissue, muscle, and bone; it is a tangible symbol for his life, for his existence on Earth, and for the impacts he made on the lives of those who loved him most.

[6] She then met with an emergency physician at the agency who introduced her to Cristal, a software that stores medical records, serves as a database of patients awaiting organ donations, matches donors with suitable recipients, and protects their identities.

[4] Finally, de Kerangal observed an organ transplant operation led by Dr. Pascal Leprince, the head of cardiothoracic surgery at Pitié-Salpêtrière Hospital.

French journalist and author Pierre Assouline referred to The Heart as "a novel of great beauty, a writing, a language dazzling" and as "fine and intelligent without ever pushing the collar.

"[9] French cultural and television magazine Télérama gave The Heart a five-star rating and commended the continuous flow and musicality of de Kerangal's prose.

In her review for The New York Times, Priya Parmar recounted the novel as a "...story [that] unfolds in an intricate lacework of precise detail" and described the characters as "less like fictional creations and more like ordinary people, briefly illuminated in rich language, beautifully translated by Sam Taylor, that veers from the medical to the philosophical.