His output includes, amongst other things, three operas, nine piano concertos, two symphonies as well as chamber and vocal music. He studied composition under the tutelage of Joonas Kokkonen, and in the 1970s he was a pupil of Witold Szalonek in West Berlin. Heiniö was appointed Professor of Musicology at the University of Turku in 1986. He has served as the composer-in-residence of the Turku Philharmonic Orchestra since 1997 and as the Chairman of the Society of Finnish Composers.