The abortion restriction was added to Senate Bill 2771, which deals with the killing of children.
Republican Andy Gipson of Braxton, chairman of the Judiciary B Committee, sponsored the heartbeat amendment, saying it would protect innocent life.
Democratic Rep. Adrienne Wooten of Jackson says the government shouldn't interfere in medical decisions made by women, their husbands and their doctors.
Detecting a heartbeat in the early stages of pregnancy can require an invasive transvaginal ultrasound.
The bill was held for more possible House debate. Because the House amended it, the bill would go back to the Senate for more work.