A catheter assembly comprises an elongated tubular outer catheter opening at its distal end, an elongated tubular intermediate catheter opening at its distal end and positioned in the outer catheter, an elongated inner catheter positioned in the intermediate catheter, and a head section provided at a distal part of the inner catheter. A deformable section serving as a stirring mechanism is provided to stir an atheroma. In use of the catheter assembly, at the time of capturing an atheroma, the deformable section is operated to stir the atheroma, and thereafter the head section slides inside the outer catheter so that the atheroma stirred by the deformable section is sucked in through the distal end of the outer catheter.
