An expandable intravascular medical device comprises an arcuate spring configured to be expanded into contact with the inner surface of a blood vessel. Another medical device comprises an electrode support structure, e.g., a non-tubular arcuate structure or a cylindrical member, and a plurality of resilient spring loops laterally extending from the support structure. The contact created between the loops and a blood vessel is sufficient to anchor the medical device within the blood vessel. In another embodiment, the medical device comprises an elongated member and two resilient spring arms extending distally from the elongated member. The arms are configured to be laterally moved towards each other to place the medical device in a collapsed geometry, and configured to be laterally moved away from each into contact with an inner surface of a blood vessel to place the medical device an expanded geometry.