The immediate cause of death was not announced, but Mr. Jansons had long suffered from cardiac ailments. In 1996, he was leading the Oslo Philharmonic, where he was music director for more than two decades, in a concert version of Puccini’s opera “La Boheme” when he suffered a near-fatal heart attack on the podium. His father, also a conductor, had died 12 years earlier in the same circumstances.
“I understood immediately that something was very wrong,” the Daily Telegraph quoted Mr. Jansons as saying. “My question was, shall I stop or can I conduct? Of course I decided to conduct. I was just thinking I must conduct very, very quietly because if I get emotional I can die. I continued for three or four minutes, then I started to feel dizzy. I remember saying to the leader: ‘I feel terrible,’ then I fell down in a faint. The players told me afterwards that my right hand went on conducting.”
He resumed his career after a long recovery, often looking weak, but rarely if ever uninspired, before an orchestra. He said that he could not live without conducting.
Mr. Jansons, who was known to American symphony-goers as music director of the Pittsburgh Symphony Orchestra from 1997 to 2004, spent very nearly his entire life steeped in music.
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His mother, a Jewish opera singer, gave birth to him in hiding during the Nazi occupation of Riga. After the war, Mr. Jansons spent much of his childhood accompanying her and his father to their rehearsals and performances.
He recalled his reaction when Don José, the leading tenor role in Bizet’s opera “Carmen,” handcuffed his mother, who was singing the title gypsy role, to take her to prison. “Don’t touch my mother!” he shouted, wailing until his father removed him from the theater. At home, the boy would array buttons and other items on his bed to form an imaginary ensemble that he would lead with a pencil in lieu of a baton.
His musical upbringing, combined with mentorship by celebrated conductors including Evgeny Mravinsky in Leningrad (now St. Petersburg) and Herbert von Karajan on the other side of the Iron Curtain, groomed Mr. Jansons for a career in the highest echelons of classical music, even as Cold War tensions in some ways limited his career.
His first major appointment, in 1979, was in Oslo. Soviet authorities, weary and embarrassed by artistic defections, had previously barred Mr. Jansons from accepting musical opportunities in the West but allowed him to take the Oslo post — on the condition that his title as “music director” remain unofficial.
“Norway was just across the border, but a different world,” he told the Independent years later. “And so expensive for me as a Russian on very limited per diems from the government. The orchestra always put me up in a good hotel, but I could never afford to eat. I used to bring my own food with me — Russian rations — except that on the first trip my food was stolen. Some introduction to a new life.”
Mr. Jansons was credited with turning the Oslo Philharmonic, where he remained until 2002, into a world-class institution. He joined the Bavarian Radio Symphony Orchestra in 2003 — succeeding Lorin Maazel, whom he also followed in Pittsburgh — and the Royal Concertgebouw Orchestra in 2004.
His unremitting international travel proved overly taxing and ultimately led him to step down from his post in Pittsburgh and work primarily in Europe. He appeared regularly with the London Philharmonic Orchestra and at the Salzburg Festival in Austria and was invited several times to conduct the Vienna Philharmonic Orchestra’s annual New Year’s concert at Vienna’s Musikverein, which PBS describes as the “largest worldwide event in classical music, reaching millions of people annually through radio and television in over 80 countries.”
On both sides of the Atlantic, Mr. Jansons was known for his rigorously prepared performances. During rehearsals, he would move throughout a concert hall, instructing musicians to scoot their chairs one way or the other to achieve what he considered the perfect sound. But those technical concerns, however important, were always of secondary interest to him.
“I was taught by perfectionists, so it goes without saying that getting the basics right is very important to me,” he told the Guardian. “Of course you ask players to play a little louder or a little quicker. But the notes on the page are only signs. You have to find what the composer wanted to express behind the notes, which in the most profound music takes you very deeply into the human condition. And if it is performed well it can be one of the most spiritually nourishing experiences imaginable.”
Mariss Ivars Georgs Jansons was born in Riga on Jan. 14, 1943. He studied the violin and later trained at the conservatory in Leningrad, where his father had been made assistant conductor to Mravinsky at the Leningrad Philharmonic.
Mr. Jansons recalled with admiration the versatility of Mravinsky’s repertoire, which ranged from Russian music to the works of Mozart, Beethoven, Brahms and Wagner. Later, in his own career, Mr. Jansons would distinguish himself similarly. He was particularly known for his interpretations of Russian composers such as Tchaikovsky, Rachmaninoff and Shostakovich, whose works he recorded in a cycle that Washington Post classical music critic Anne Midgette described as “a benchmark and a cornerstone of any record collection.”
But Mr. Jansons was equally capable conducting the works of Haydn, Mozart, Beethoven and Schubert. Writing in the Guardian, music critic Barry Millington lauded his “lacerating anguish in Mahler symphonies, blistering climaxes in Strauss tone poems, intense, finely wrought detail in almost any repertoire,” describing them as “the characteristics that defined his music-making, which consistently pushed expressive possibilities to their extremes.”
A prize in von Karajan’s international conducting competition boosted Mr. Jansons’s profile in the early 1970s. Like his father, he was an assistant conductor at the Leningrad Philharmonic before accepting his position in Oslo, where he began to make his international reputation.
In 2017, Mr. Jansons caused a stir when he remarked to a reporter for the Daily Telegraph that he “grew up in a different world, and for me seeing a woman on the podium . . . well, let’s just say it’s not my cup of tea.” He later apologized.
The Telegraph reported that he was divorced from his first wife, Ira, with whom he had a daughter, Ilona, who became a pianist. He was later married to Irina Outchitel. A complete list of survivors was not immediately available.
Mr. Jansons’s health was so poor of late that during at least one recent performance an ambulance was stationed nearby. His ailments, while sometimes making it a struggle for him to complete a performance, brought an added poignancy to the sound that he coaxed from his musicians.
“I think you become a more profound person,” he told the Guardian in 2007, reflecting on the heart attack he suffered during “La Boheme.” “I started to like more quiet music, definitely; I started to enjoy performing more profound music, more slow tempos. But you have to forget about it as well — you can’t always think about that experience, even if, from a medical point of view, you must never forget.”
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