In the season finale of "Heartbeat," Alex fights to save the lives of Jesse, Pierce and Ji-Sung when a mysterious and deadly illness sends the hospital into lock down. Meanwhile, Millicent must pick up the pieces when Alex disobeys the orders of the CDC, and an elderly man searching for his missing wife leads Alex to make a drastic decision in her love life.

Alex and Jesse put the hospital's reputation on the line while trying to fulfill the dying wish of a young heart patient.

When Alex's father needs a new kidney, an unlikely donor emerges and family secrets threaten to destroy the close relationship between father and daughter.

When a transgender woman is diagnosed with breast cancer, Alex and Ji-Sung fight to save her life and her identity. Meanwhile, a beautiful consultant from another hospital forces Jesse to confront his feelings for Alex.

A case brings back memories for Alex, Jesse and Millicent when they try to save a heart transplant patient who sustained devastating injuries in a car crash.

On the anniversary of her sister's death, Alex performs heart surgery on a patient who fears she can't leave her personal grief out of the operating room. In other events, Millicent dates a sexy artist; and Pierce wants a bigger role in Alex's family.

Alex and Pierce disagree on whether an experimental treatment for those with advanced stage cancer is right for the hospital's patients. True to form, Alex takes matters into her own hands with a risky move to find volunteers. Meanwhile, Max looks to drastically change the family dynamic with Alex, and Ji-Sung connects with Callahan.

While working with a patient who can only speak backwards, Alex also finds herself challenged to speak when she and Pierce, after being caught in a compromising position, are sent to therapy.

Alex suggests risky surgery for conjoined twins with cancer; and she questions her relationship with Pierce.

Heart-transplant surgeon Alexandra Panttiere, who's as unorthodox in the OR as she is with the two men in her life, takes on a new case.