The news
Scientists have grown a piece of heart muscle — and then watched it beat — by using stem cells from a mouse embryo.
This is a big step toward repairing damage from heart attacks .
Dr. Kenneth Chien and his team from the Harvard and Massachusetts General Hospital researchers said “We’re making a heart part and (eventually) we’re going to put the part in”.
Lots of work remains before trying that experiment in people but regenerating damaged heart muscle is a holy grail in cardiac care.

Why is this important?
Doctors today have lots of treatments to prevent a heart attack. But once it strikes, there’s no way to restore the heart muscle it kills. Gradually the weakened heart quits pumping properly, leading to deadly heart failure .
Hence the focus on embryonic stem cells, master cells that can give rise to any tissue in the body. Until now, scientists haven’t known how to turn master cells into producing pure cardiac muscle .

Previous attempts were a failure
Up to now, researchers have tried injecting heart attack survivors with mixes of different kinds of stem cells, next-generation types like those found in bone marrow. The idea was that perhaps once those cells were inside a damaged heart, ones capable of growing cardiac muscle would receive a “get to work” signal and take root. But that was not successful.
The new research , published in Friday’s edition of the journal Science, is a more targeted approach.

How did they do it
The team genetically engineered mice so that certain cells in the embryos’ developing hearts would light either fluorescent red or green. As they watched the embryos grow, an overlapping of colors signaled developing heart muscle. When the team plucked out those cells, they were pure ventricle generators, which is not enough.
Next the team cultivated the stem cells and a thin strip of mouse heart muscle grew on the top of the cell. What happened next is that the muscle started to beat by itself. The best thing about this is “This looks like the kind of work a normal heart tissue strip would do,” said Dr Chien “We went from embryonic stem cells to an organ.”

Is it portable to humans?
Yes because what the team has done is to use a mice stem cell that is present in both human and mouse embryos.

What’s next
This was not a fully developed piece of heart muscle but only a thin strip.
To be usable, it would have to be thicker, more three-dimensional, for more beating strength. It also needs a nourishing blood supply. So a next big challenge is pinpoint which one of those master heart stem cells can grow into blood vessels.

Opportunities
The experiment offers a possible new opportunity for cell therapy.
The team will now develop two approaches. Either they can try and develop cells outside of a body to a full heart and them implement that in a human body or they can try to inject the cells onto the heart once a muscle has developed and see if that helps.