Born in Liberec, Hejnova established her heptathlon history in 1999 with a silver-medal performance at the European Junior Championships in Riga, Latvia, producing a total score of 5786 points. Four years later, Hejnova highlighted her sporting career on the world stage at the 2003 Summer Universiade in Daegu, South Korea, where she claimed the bronze behind Australian duo Kylie Wheeler and Jane Jamieson in the women's heptathlon with a score of 5795 points.