Healing the hearts of men and gorillas
8 April 2013 Last updated at 02:07 BST
Larry Hergott is a cardiologist at the University of Colorado. He believes that "medicine is poetry, more than a profession".
Fourteen years ago, he got a phone call from the Denver zoo. Despite never having worked with big apes, he was asked to work with veterinarians to check the animals' hearts.
The zoo veterinarian explained that a gorilla's heart is similar to a human heart, and that the zoo badly needed a human cardiologist to help complete their care.
Primates held in captivity are at increased risk of death from heart-related disease. They can get high blood pressure, high cholesterol and heart failure.
As soon as he visited his first 515-pound patient, an orangutan named Kandu with a family history of heart disease, Hergott was fascinated by the experience.
"Once you are in their presence you get this connecting and soulful experience that is hard to describe," he says. Since then, the cardiologist has divided his time between human and ape patients, which he treats free of charge.
The zoo staff has trained the gorillas to go through the basic electrocardiogram without being anaesthetised. They offer their chests through the cage, while a nurse feeds them peanuts.
The BBC spent a day with the "gorillas' cardiologist" while he visited his big patients at the zoo.
Produced by Anna Bressanin, Images by Ilya Shnitser.