Merten won three medals in his breaststroke specialty at the Pan American Games.

[1] At the 1963 Pan American Games in São Paulo, Brazil, he won a silver medal for his runner-up finish in the 200-meter breaststroke.

[1] Four years later at the 1967 Pan American Games in Winnipeg, Manitoba, he received a pair of bronze medals for his third-place performances in the 100-meter and 200-meter breaststroke.

[1] Merten represented the United States at the 1968 Summer Olympics in Mexico City.

[2][3] He also swam in the preliminary heats of the men's 200-meter breaststroke, clocking a time of 2:37.0, but did not advance.