This work describes the design of two devices for measuring the blood volume changes, in the forearm with a portable device and in the thighs through clothes in seated position. When blood volume arrives to the measurement site from the left ventricle, the electrical properties of the body segment change. These changes, that mainly comprise the electrical impedance of the tissue, are measured through the injection of a safely ac current and the detection of the voltage changes due to blood flow. The signal recorded with such a method is the impedance plethysmogram (IPG). For the portable device, an analog processing converts the IPG waveform to square pulses and a microcontroller performs the on-line estimation of the heart rate. Accuracy of the results accomplishes the standards of the Association for the Advancement of Medical Instrumentation for heart rate monitors. When measuring the IPG in the thighs through clothes, on the other hand, the main inconvenient are the stray capacitances that modify the waveform of the measured signal. However, with the proper cares, the waveform is good enough to extract the heart rate in the post processing.