Flow boiling is a propitious technique for numerous heat transfer applications, although many questions remain unsolved about the occurring phenomena and reliability. One of the facets that required further research is the effect of a time-varying heat flux on the heat transfer performance. Therefore, this study discusses the effects of a square waveform heat flux profile on saturated flow boiling of R245fa in a horizontal test section. The cylindrical test section was made of stainless steel with an inner diameter of 17.12mm. Heat was supplied uniformly around the tube by constantan resistance wire through which a current was sent. The resulting parameters of interest were the wall temperature of the test tube, measured by 80 thermocouples inserted in the tube wall, and the inner wall heat transfer coefficient, which was deducted from the thermocouple measurements and imposed heat flux. The test matrix was created so that the influence of oscillation period and oscillation amplitude could be tested for a setpoint in the annular flow regime, with a mass flux of 200kg/m^²s and an inlet vapor quality of 0.5. The considered average heat flux was 12.09kW/m^². It was found that the heat transfer characteristics followed the same oscillation frequency as the imposed heat flux, although their reaction had a small delay attributed to the thermal capacity of the tube material. Both a longer oscillation period and a larger oscillation amplitude provoked heavier oscillations of temperature and heat transfer coefficient. The results suggested that for the considered setpoint, the heat transfer performance under the square waveform heat flux profile slightly exceeded the performance under constant heating, although further research is needed to confirm this finding.