Surgeons transplanted a new heart into a boy less than a month old, replacing a defective organ discovered before his birth, a hospital spokeswoman said. Daniel Jirschefske, born Sept. 26 to a Pasadena couple, received his new heart in a 5 1/2-hour operation performed by a team of Loma Linda Medical Center surgeons headed by Dr. Leonard Bailey, the spokeswoman said. Baby Daniel was in critical condition after the surgery, the 22nd heart-transplant operation performed at Loma Linda on an infant under the age of six months. Eighteen of the infants have survived. Susan and David Jirschefske appealed to the public earlier this month for help in finding a donor heart for their baby, whose potentially fatal heart underdevelopment was discovered while he was still in his mother’s womb.