The Cardinals have the heart of their defense back on the field.

The team activated Tyrann Mathieu from the physically unable to perform list on Tuesday, the Cardinals announced on their website. He returned to practice after posting the following message to his Twitter account:

Head coach Bruce Arians cautioned that the activation of Mathieu (along with Justin Bethel and Frostee Rucker) doesn't necessarily mean he'll be active for Week 1, but he did note that Mathieu's knee is getting stronger.

"We have the computers on him which tells the strength in each leg," Arians said, per the team's website. "He's real, real close."

Mathieu is coming off the second torn ACL of his career, which he suffered during a Week 15 win over the Eagles. He had previously torn the ACL and LCL in the opposite (left) knee back in 2013.

While he's had two of his three NFL seasons cut short, Mathieu has been a star when he's actually been on the field. He was one of the handful of best defensive players in all of football last year, and he was rewarded with a huge extension earlier this summer.