Šejna's musical studies were at the Prague Conservatory under Professor Černý (double-bass, 1914–20) and later with K. B. Jirák (composition).
He began to conduct on recommendation of the principal conductor of the Czech Philharmonic of that time, Václav Talich.
Talich gradually entrusted him with more difficult tasks, and later recommended him to the post of conductor of the Czechoslovak Railway Workers Symphony Orchestra (1925–1936).
He was a noted interpreter of the music of Hector Berlioz, César Franck, Richard Strauss and especially of Gustav Mahler.
[3] His 1959 recording of Dvořák's Slavonic Dances was awarded Cithare d´argent - Grand Prix de l´Association Française in Paris 1977.