Ella Fitzgerald sang to a sellout crowd at New York's Avery Fisher Hall Wednesday, her first major concert since she was hospitalized with a heart ailment last year. Fitzgerald, backed by her regular trio and another longtime collaborator, guitarist Joe Pass, said, "I am so happy to be singing--you don't know. I thank the miracle man above." She received a standing ovation the moment she walked on stage. Fitzgerald was sidelined for nearly nine months after she was hospitalized last July 27 for congestive heart failure after a concert in Niagara Falls, N.Y. After returning to Los Angeles, she underwent a quintuple bypass operation.