A mountain lion attacks a young woman.

A jewelry shop owner undergoes open-heart surgery after being shot during a robbery.

Dr. Keller thinks a boy struck by a baseball bat has a concussion, but a CT scan reveals massive brain bleeding, and he suffers kidney failure.

An 11-year-old girl has streptococcal pneumonia, which has a high fatality rate.

A tornado slams a fence picket into a woman's head.

A 7-year-old boy undergoes surgery to reattach his left arm after it was severed in a truck accident.

A teenager rushes to the ER after a football game.

An automobile accident critically injures a driver.

A stack of drywall collapses on a young boy.

A crazed gunman storms a large metropolitan hospital and opens fire in the ER.

A car accident ejects a young boy from a vehicle.

A team of doctors tries to save a patrol officer's life.

A rattlesnake bites the 2-year-old son of a snakebite expert.

A ruptured brain-aneurysm threatens the life of the ER's medical director.

A surgical resident puts her training to the test when a mugging survivor arrives with two bullet wounds.

A seemingly healthy baby suddenly develops an oxygen deficiency.

A construction worker's skull has a 4-pound hook embedded in it and a trauma surgeon struggles to extract it without killing him.