"I'm so excited to welcome @ashleytisdale to my new show , #CarolsSecondAct on @CBS! So talented, so sweet, so funny, so normal!" Heaton tweeted Friday.
Heaton, who is best known for her work in the family comedies The Middle and Everybody Loves Raymond, will play a retired teacher who decides to become a doctor.
Deadline.com said Tisdale is replacing Bonnie Dennison, who co-starred in the pilot as Jenny, a pharmaceutical representative and the title character's daughter.
No reason was given for the casting change.
The show will also co-star Kyle MacLachlan, Ito Aghayere, Jean-Luc Bilodeau and Sabrina Jalees.