The results are a boost to scientists who hope to one day use a similar technique to repair or replace damaged hearts and other organs in humans.
"The idea would be to develop transplantable blood vessels or whole organs that are made from your own cells," lead researcher Doris Taylor, director of the Center for Cardiovascular Repair at the University of Minnesota, told AFP.
In the study, Taylor and her colleagues used detergents to strip away all of the cells from a dead rat heart, leaving only a scaffolding of proteins.
"It looks like a ghost heart," said Taylor.
Then, the researchers reseeded the scaffolding with heart cells from newborn rats. In just eight days, and with an electrical jump-start, the cells grew into a new, beating heart that pumped some blood--about two percent of the amount of blood pumped by an adult rat heart.
"When we first saw the contractions, we were speechless," said researcher Harold Ott, of Harvard Medical School.
To test whether the lab-grown hearts would be rejected by a live rat, the researchers transplanted the hearts into the abdomens of unrelated rats. The hearts continued to beat in the rats abdomens, and developed a blood supply.
The researchers hope to someday use the technique to grow a human heart by seeding a cadaver heart with stem cells taken from a patient's bone marrow, according to the New York Times. Such a heart would have less chance of being rejected by the patient's immune system than a donor heart. The technique might even be used to create other organs as well, Taylor told the New York Times.
The research "opens the door to this notion that you can make any organ: kidney, liver, lung, pancreas -- you name it and we hope we can make it," she said.
However, both Taylor and other researchers say that day is a long way off--at least 10 years away, Taylor told the New York Times.
For now, the researchers are scaling the study up and conducting similar research on pigs, an animal whose heart anatomy is more similar to humans.