Methods and apparatus are provided for repairing or replacing a defective cardiac valve including an anchor having a double helix configured to engage the cardiac valve leaflets of a diseased or defective cardiac valve, and a replacement valve body disposed in an expandable stent configured to be disposed within the anchor so that the anchor limits expansion of the expandable stent. The expandable stent of the replacement valve body may be self-expanding or mechanically expanded, e.g., using a balloon catheter or catheter-based mandrel and the valve body may be formed of animal tissue or a synthetic fabric.