A system for obtaining signals related to electrical activity of the heart of a subject includes a sensing device including an elongate member having a distal end configured for placement within a body lumen of a subject, and a proximal end configured to extend from the subject, an actuation portion carried by the elongate member and configured for placement within the body lumen, the actuation portion having a low-profile state for delivery within the body lumen and an expanded state, and one or more sensors disposed on the actuation portion, each including a contact surface configured to contact an interior wall of the body lumen, wherein the actuation portion is configured to cause the contact surface of each of the one or more sensors to contact a location on the interior wall of the body lumen to provide a signal component for producing one or more electrocardiogram signals.