CHA Hollywood Presbyterian Medical Center in Los Angeles operated on a 25-week old fetus with severe aortic stenosis "after practicing a few times with a model of jello and a grape — the grape standing in for the heart, the jello standing in for the surrounding body."

The heart of a fetus this young is "about the size of a walnut," writes Deborah Netburn at the Los Angeles Times.

There's video below, and a detailed explanation of how the procedure worked, at latimes.com.

[latimes.com via FARK]