This paper presents emergent experimental results showing that mental effort of programmers in code understanding tasks can be monitored through HRV (heart rate variability) using non-intrusive wearable devices. Results suggest that HRV is a good predictor for cognitive load when analyzing code and HRV results are consistent with the mental effort perceived by programmers using NASA-TLX. Furthermore, code complexity metrics do not correlate entirely with mental effort and do not seem a good indicator of the subjective perception of complexity felt by programmers. These first results are presented in the context of the project BASE-Biofeedback Augmented Software Engineering, which is briefly sketched, and proposes a radical neuroscience enabled approach to introduce biofeedback in software development.