The variation of pressure of the blood is a key parameter in the development of ventricular assist device. This latter is useful in order to synchronize the behavior of the actuator with the cardiac frequency. This paper presents a sensor made of a dielectric electroactive polymer (DEAP). A particularity of this sensor is the special tubular shape, similar to an aorta, which allows to be used for medical application. The sensor is based on the measurement of the variation of the capacitance of the DEAP because of the inner pressure. An analytical model is proposed to explain the deformation of the thin membrane. A feature of the model is to take into account the boundary conditions of the cylinder that causes a particular curve to the inflated cylinder. The analytical equations for the inner and outer radius variation of the inflated tube are proposed in order to define the variation of the surface and the thickness of the sensor. The study of the stress in the membrane is done to link the internal pressure to the geometrical model of the deformation. The mean error between the pressure measurement and the value deduced from the analytical model according to the capacitance is around 7%. The analytical model is better for higher pressure with a mean error of 2.4% from 80 Pa.