A catheter includes an elongated body having a longitudinal axis, a distalassemblydistal the elongated body, the distal assembly having a tapered helical formcomprising a larger,electrode-carrying proximal loop and a smaller, softer distal loop, and ashape-memory supportmember extending through at least the proximal loop. For example, the helicalloop subtendsat least about 720 radial degrees, with the proximal loop subtending about 360radial degrees,and the distal loop subtending about 360 radial degrees. The softer distalloop with a straightdistal end atraumatically guides the distal assembly into a tubular region sothat the largerproximal loop can sit on the ostium of the tubular region with improvedelectrode and tissuecontact.
