A leadless intravascular sensor (100, 200) uses the body tissue as a communication medium. The implantable intravascular device has a tubular stent-like structure (102) for intravascular fixation with embedded microcircuits to allow bipolar and unipolar sensing of cardiac and neurologic electrical activity, sensing of other physiologic signals, local electrical stimulation (cardiac pacing and defibrillation; neurologic stimulation and seizure therapy) as well as the ability to communicate with other implanted and non implanted devices via radio frequency and/or optical communication and/or analog signal communication using the body tissue as the conducting medium. The device can also be used in the extravascular or perivascular space. In this form, it has an open/flexible ring that can be adjusted, or self-adjusts to provide no pressure or required contact around the vessel or target region.