Mission, Texas - Eddie Longoria's first 13 days of life - difficult days for the premature infant - were set to a soft, soothing soundtrack of jazz and classical music.

Above his warming table/crib at Mission Regional Medical Center's neo-natal intensive care unit, a high-end speaker piped in tunes that doctors say help the hospital's youngest patients thrive and their caretakers relax.

"The NICU by default is a very stressful environment," said Dr. Anatoliy Ilizarov, the unit's medical director. "The music helps to pacify the situation."

The walls of the NICU are cheerful pastels, but this is no ordinary nursery. The babies here, who for a variety of reasons left their mothers' wombs too soon, are struggling to grow and survive in the outside world.

Longoria's parents, Belinda and Eduardo, had planned to bring Eddie home to their other two children, 9 and 4, soon after his birth. Instead, their early bird ended up here, attached to a nest of wires and monitors, fighting off infection. To hold him, Belinda had to scrub her hands for three minutes, like a surgeon.

"We usually come twice or three times a day," she said. The Mission resident said she hardly notices the music anymore.

"It's relaxing, so it helps," she said, her eyes on her son. He weighed 5 pounds - nearly a pound more than when he was born six weeks early, but still lighter than doctors had hoped. Downy black hair stretched down his back, further evidence that he hadn't been carried to term.

Nearby, one of a set of newborn triplets slept through Eddie's occasional, fitful cries, a tiny arm flung over the edge of his cradling pillow.

In this environment, music serves multiple purposes, Ilizarov said.

It calms and focuses doctors and nurses, cutting through the sterility of the environment and the stress of caring for such vulnerable patients to soothe frazzled nerves.

But the major benefit may be to their tiny convalescents. Medical research indicates premature infants grow faster and begin normal feeding patterns sooner when they are exposed to soft music.

The reasons for this are still unclear, Ilizarov said. One theory is that the tempo of the music - generally between 60 and 80 beats per minute - mimics the maternal heartbeat familiar from their months in utero. After the assault of light and sound, cold temperatures and hard or rough surfaces, a reminder of the womb can help the youngest finish the development stages they weren't able to due to their early arrival.

"I try to find music that is not too adagio, but you don't want to go crazy with the allegretto, either," joked Ilizarov, who was trained as a concert pianist and uses the Italian words for slow and speedy tempos that are common musical notations.

Still, the music is a strange addition when compared to the amount of trouble to which NICUs go to maintain a quiet environment.

Loud noises can cause permanent hearing loss and other damage to preemies. The American Medical Association recommends noise levels below 50 decibels - which, Ilizarov said, is about the volume of the air conditioning system alone.

Mission Regional used to have decibel monitors along the wall to remind visitors to be quiet, but last year replaced them with easy-to-read stoplight-style indicators. Yellow lights warn the noisy; a flash of red light means sound levels are over 65 decibels - "Shhhhh."

Ilizarov said he also programmed quiet hours into the musical system.

"None of us is intended to listen to music all the time," he said. "It'll drive you crazy."

Staff members have some latitude in choosing their daily accompaniment. Some pediatricians have their own, preferred playlists on the unit's central computer, labeled "Baby - Jazz," "Baby - Bossa Nova" and "Baby - Paul Mauriat."

Ilizarov is partial to popular piano music from his native Russia.

Nurse Leticia Cano said the music certainly can't hurt, even if it doesn't help. "If it's relaxing for the nurses, it must be relaxing for the babies," she said.

Some parents expose their children to classical music at an early age, hoping to boost cognitive development or even cultural appreciation. But Belinda Longoria just wanted to see her Eddie allowed to leave the confines of the NICU.

Two weeks ago, he did, meeting his older siblings for the first time.