Competing in three Summer Olympics, he who won two silver medals at Sydney in 2000 (K-1 500 m, K-1 1000 m).

Prior to those games, Merkov was subjected to controversy for failing a doping test in Bulgaria which led to over a dozen canoeing nations petitioning the International Canoe Federation for an investigation, only to have Bulgarian officials stonewall on his behalf to compete.

He would later refuse to attend the post-race press conference of K-1 1000 m in the wake of those allegations.

At the ICF Canoe Sprint World Championships, Merkov won silver medals in the K-1 500 m event in 1999 and 2002.

In 2002, he also won a bronze in K-4 1000 m. Merkov is 188 cm (6'2") tall and weighs 95 kg (209 lbs).