Studying initially at the University of Helsinki and the Sibelius Academy with Einojuhani Rautavaara, Heininen also spent time at the Juilliard School and in Poland where he took private lessons from Witold Lutosławski.
Heininen's works often incorporated serialist and twelve-tone techniques and were not always universally loved. For instance, the orchestra that gave the premiere of Heininen's First Symphony refused to perform the work's second movement, playing only the two outer movements instead.
Some of his works were perceived as much more approachable, however, and this quality is epitomized by the Second Symphony, subtitled "petite symphonie joyeuse."
Perhaps somewhat unusual for a composer working in the mid-to-late twentieth century, Heininen was a prolific symphonist and wrote eight symphonies by the time of his death. He was also a strong contributor to vocal music and greatly enjoyed setting texts; among these works were his two operas The Knife and The Damask Drum.
Alongside his work as a composer, Heininen was also an influential teacher of composition. He held a professorship at the Sibelius Academy from 1993 to 2001, having worked there part-time since 1966. Over the course of those four decades, he taught some of today's most prominent Finnish composers, including Kaija Saariaho.
Towards the end of his life, Heininen was diagnosed with cancer and he passed away on January 19 in a nursing home in Järvenpää. Our condolences to Heininen's family, friends, and colleagues.