A pressure-driven flexible fiber nanogenerator (FNG) is demonstrated that can be used for smart shirts, flexible electronics, and medical applications. An output peak voltage of 3.2 V and average current density of 0.15 mu A cm(-2) are demonstrated. The pressure-driven FNG added to a syringe shows potential to harvest energy in a blood vessel, as well as in gas pipes and oil pipes. The heart-pulse driven FNG can serve as an ultrasensitive sensor for monitoring the behavior of a human heart for medical diagnostics.