Note to teachers: Some of the medical procedure images in this video are graphic.

As a result of heart attacks, doctors across the U.S. are trying to keep alive more than five million Americans with damaged hearts.

When the heart muscle cells are deprived of oxygen during an attack, scar tissue forms in the heart, and it doesn't work like the other heart cells do.

Now, in what they consider a dramatic development, scientists at the Gladstone Institutes in San Francisco have figured out a way to transform damaged tissue into functioning heart muscle in mice.

They gave the lab mice mild heart attacks and then tricked the tiny mouse hearts into rebuilding themselves.

The big question is: Will this technology work in humans?

Researchers are excited about this possibility, but they have to make sure it's safe to do so. According to the report, scientists will likely use a larger animal model that's closer to human, such as a pig.

Dr. Deepak Srivastava, who directs cardiovascular and stem cell research at Gladstone, estimates it will be six or seven years before treatments might be available for humans.

"We have to make sure that it's scalable to the size of a human heart where, where instead of thousands of cells that we might need to regenerate in the mouse, we may need millions in the human heart," - Dr. Deepak Srivastava.

1. What is oxygen?

2. What happens to the human heart when it doesn't receive oxygen?

3. What is scar tissue?

1. What do you think about this scientific discovery?

2. Do you know anyone who's suffered from a heart attack and might benefit from this treatment?

3. What are your thoughts about testing the procedures on animals first? Do you agree or disagree with this practice? Discuss.