New York researchers transplanted pig hearts into two brain-dead people over the last month, the latest in a string of developments in the long quest to one day save human lives with animal organs.

The experiments announced Tuesday come after a historic but failed attempt earlier this year to use a pig’s heart to save a dying Maryland man — sort of a rehearsal before scientists try again in the living.

Among the lessons: Practice with the deceased is important.

“We learned so much from the first one that the second one is much better,” said Dr. Nader Moazami, who led the operations at NYU Langone Health. “You stand there in awe” when the pig heart starts to beat in a human body.

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This time around, Moazami’s team mimicked how heart transplants routinely are done. Once last month and once last week, researchers traveled to a facility housing genetically modified pigs, removed the needed hearts, put them on ice and flew them hundreds of miles back to New York.

They used special new methods to check for any worrisome animal viruses before sewing the heart into the chest of each deceased recipient — a Vietnam veteran from Pennsylvania with a long history of heart disease and a New York woman who’d benefited from a transplant earlier in life.

Read more: AP