Common to many microfluidic chips is narrow constriction as inlet and outlets which need to be accessed by needles. Part of the reason for the use of these narrow constriction is to reduce sample evaporation. However, would narrow constriction affect the viability of cells as they are pipetted into the microchannels? This work aims to investigate this issue using a PMMA microfluidic chip with narrow constriction with Escherichia coli DH5α as model organism. Specifically, stationary phase E. coli cells were pipetted into the microfluidic channel for a 10 minutes exposure. Subsequently, the cells were pipetted out through the same narrow constriction. Results indicated that there is a substantial drop in cell viability after passing through the narrow constriction twice. Overall, the preliminary results presented in this work suggests that there is a drop in cell viability after passage through narrow constriction in microfluidic chips which reveals that we may be selecting for fitter cells in our microfluidic cell growth experiments. Such effect may skew our conclusions particularly with drug dosage experiments conducted on microfluidic chips where fitter cells may need a higher drug dosage or more toxic drugs for killing.