- Doctors and medical students
- Sam Anderson as Dr. Jack Kayson – Chief of Cardiology
- John Aylward as Dr. Donald Anspaugh – Surgeon and Hospital Board Member
- Leland Orser as Dr. Lucien Dubenko – Attending Surgeon, later Chief of Surgery
- Scott Grimes as Dr. Archie Morris – Resident PGY-3
- Sara Gilbert as Jane Figler – Fourth-year Medical Student
- Eion Bailey as Jake Scanlon – Medical Student
- Lou Richards as Dr. Perkins
- Francesco Quinn as Dr. Alfonso Ramírez
- Andy Powers as Dr. Howard Ritzke
- Norbert Weisser as Dr. Adler
- Anthony Giangrande as Dr. Jeremy Munson – Intern PGY-1
- Michael Spellman as Dr. Jim Babinski – Intern PGY-1
- Giovannie Espiritu as Ludlow - Medical Student
- Nurses
- Deezer D as Nurse Malik McGrath
- Laura Cerón as Nurse Chuny Márquez
- Yvette Freeman as Nurse Haleh Adams
- Lily Mariye as Nurse Lily Jarvik
- Dinah Lenney as Nurse Shirley
- Bellina Logan as Nurse Kit
- Kyle Richards as Nurse Dori Kerns
- Liza Del Mundo as Nurse Severa
- Sumalee Montano as Nurse Duvata Mahal
- Nadia Shazana as OR Nurse Jacy
- Tane Kawasaki as Nurse Claire
- Mary Heiss as Nurse Mary
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- Staff, Paramedics and Officers
- Abraham Benrubi as Desk Clerk Jerry Markovic
- Mädchen Amick as Social Worker Wendall Meade
- Troy Evans as Desk Clerk Frank Martin
- Pamela Sinha as Desk Clerk Amira
- Jordan Calloway as Hospital Volunteer K.J. Thibeaux
- China Shavers as Olivia Evans from Ceasefire
- Emily Wagner as Paramedic Doris Pickman
- Montae Russell as Paramedic Dwight Zadro
- Lyn. A Henderson as Paramedic Pamela Olbes
- Brian Lester as Paramedic Brian Dumar
- Michelle C. Bonilla as Paramedic Christine Harms
- Demetrius Navarro as Paramedic Morales
- Louie Liberti as Paramedic Bardelli
- Meg Thalken as Chopper EMT Dee McManus
- Chad McKnight as Officer Wilson
- Family
- Thandie Newton as Makemba "Kem" Likasu
- Henry O as Mr. Chen
- Renee Victor as Florina Lopez
- José Zúñiga as Eduardo Lopez
- Donal Logue as (Flight Nurse) Chuck Martin
- Oliver Davis as Alex Taggart
- Garret Dillahunt as Steve Curtis
- Anupam Kher as Ajay Rasgotra
- Kiron Kher as Mrs. Rasgotra
- Frances Fisher as Helen Kingsley
- Danny Glover as Charlie Pratt
- Sam Jones III as Chaz Pratt
- Hassan Johnson as Darnell Thibeaux
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