Nicola Rescigno, the co-founder of the Dallas Opera and one of Maria Callas' favorite conductors, has died at a hospital in Italy, officials said Tuesday. He was 92.

Rescigno died Monday of complications following heart failure and breathing problems, said Corrado Ricci, a doctor at the Belcolle hospital in Viterbo, a town about 50 miles north of Rome. Rescigno had been admitted on July 30 with a broken femur, following a fall. But Ricci said that at that point, he was already in serious condition.

Jonathan Pell, the Dallas Opera director of artistic administration, said he received a call Monday afternoon from Rescigno's nephew, who had been informed of his uncle's death by the hospital.

Pell said Rescigno "went to sleep and didn't wake up."

The New York-born Rescigno moved to music after a receiving a law degree at Rome's La Sapienza university. His career was largely spent in the United States.

He conducted Callas' debut in America, eventually becoming one of the star soprano's favorite conductors throughout a cooperation that spanned several years, performances and recordings.

"He knew how to bring together orchestra and singing, doing everything possible to bring out the best singing performance," said Elvio Giudici, a leading opera critic. "It is not by chance that he worked with Callas when she had her small vocal problems."

Rescigno and the late Lawrence V. Kelly founded the Dallas Opera in 1957, with Rescigno taking the job of artistic director.

According to the theater's Web site, the theater opened with a concert by Callas in November of that year.

After Kelly's death in 1974, Rescigno took on the role of general director as well.

Rescigno was also a co-founder of the Lyric Opera of Chicago and conducted at the Royal Opera Covent Garden, Metropolitan Opera and Vienna State Opera. His recordings include recitals with Callas and Luciano Pavarotti.

During his career, Rescigno also toured some of the most important opera theaters in Italy, including Rome's Opera House, the San Carlo in Naples and La Fenice in Venice.

"He was of the old school. He knew the repertoire backwards," said Giudici. "He could solve any problem because he knew the subject really well."

"Adjust the sound, the orchestra, the timing, the dynamics to the conditions of any given night: this is something that old-time directors could do really well," said Giudici.

Pell said plans to honor Rescigno by the Dallas Opera will be announced later.