As the heart expands and contracts, the distance between the walls of the heart and the surface of the body changes continuously. This structural change causes the dielectric constant of the body to vary. To detect that variation, a capacitance-variation detector with a high sensitivity on the order of 100 aF has been developed. It employs an LC-oscillator architecture with 98 MHz, and the change in capacitance is determined from the oscillation frequency shift. Experiments demonstrated that it detected the movement of the heart of an actual person from the frequency shift. The system detects not only heart-beat count but also the real movement of heart itself.