An arm-worn electrocardiographic device in a shape of a band, comprising a measurement module for processing the measured electrocardiographic signal, characterised in that the first measuring wing (2) and the second measuring wing (3) are attached to the measurement module (1), symmetrically with respect to each other, by means of spring connectors (7, 8), for measuring the electrocardiographic signal, and a first fastening strip (4) and a second fastening strip (5) are attached to each of the measuring wings (2, 3), respectively, by means of spring connectors (6, 9), wherein the module (1), the measuring wings (2, 3), and the fastening strips (4, 5) have an inner surface for contacting the user's skin and an outer surface for attaching the personalizing attachment (26), and on the inner surface of the module (1) a third electrode (10) is located, on the inner surface of the first measuring wing a first second electrode (11) is located, and on the inner surface of the second measuring wing (5) a second third electrode (12) is located, wherein each of the electrodes (10, 11, 12) comprises a matrix (15, 50, 51) of movable sensors (16), respectively, wherein the surface area ratio of each electrode (10, 11, 12) to the surface area of the inner surface of the first fastening strip (4) or the second fastening strip (5) is not greater than one, wherein the movable sensor is comprised of a conductive material (16a) bonded to an elastic substrate (14).