A medical device for breaking up and aspirating material, especially intravenous clots, having a catheter, a barrel, and a sheath is disclosed. The catheter has a lumen through which material is aspirated. The barrel has a first and second end connected by a plurality of blades that are self-biased to extend outward. The sheath provides a selective radial constraint such that the blades are constrained when the sheath covers the barrel and unconstrained when the sheath is retracted.
