In 1983, Kratochvílová broke the 800 m world record with a time of 1:53.28. At the World Championships shortly afterwards, she won the 800m and set a world record of 47.99 seconds to win the 400m.
Kratochvílová's 1983 400-metre world record of 47.99 seconds stood for only two years until it was broken by her great rival Marita Koch in 1985. Koch's 400-metre world record of 47.60 seconds still stands as of 2018. Koch and Kratochvílová are the only women who have broken the 48 second barrier in a 400-metre laned race. Her 800-metre world record is the longest standing track record in men or women's athletics, and was described by 1996 Olympic champion Svetlana Masterkova as ".. very fast. It's impossible for women to run so fast. It will last for 100 years."
Kratochvílová was a late developer, not breaking 53 seconds for the 400 metres until she was 27, and she was 32 when she set her world records. Her remarkably fast times, and her atypical muscular physique spawned rumors of illegal drug use. Kratochvílová has maintained her innocence, and although in 2006 the Prague newspaper Mladá fronta DNES claimed to have uncovered a doping program run by Czechoslovakia's Communist government, there was no link to Kratochvílová despite her being her country's highest profile athlete. She and her coach of 20 years, Miroslav Kvac, maintain that it was rigorous training and high doses of vitamin B12 that account for her records.
Since her retirement the 67 year old Kratochvílová has worked as an athletics coach and with the Czech national team. She has never failed a drug test.
