A deltamethrin selected field strain of the house fly, Musca domestica, was used to assess realized heritability (h2) and risk for resistance development to deltamethrin. The estimated value of h2 was 0.27 with phenotypic standard deviation σp = 0.56 and selection differential S = 0.64. The intensity of deltamethrin selection had a direct effect on the rate of resistance development in the selected strain. Assuming the h2 value = 0.27 for six generations under selection pressure, a tenfold increase in the LC50 values has been expected in only 8-4 generations at the selection intensity 50–90%, respectively. In conclusion, the estimated values of h2 and the projected rate of deltamethrin resistance revealed a strong and rapid potential of the M. domestica strain to develop resistance against deltamethrin. Therefore, this insecticide should be used cautiously in the field.