HeartMate II and HeartMate 3 devices are being recalled because a buildup of biological material is obstructing the device, making it more difficult for the heart to pump blood.

http://www.fda.gov/medical-devices/medical-device-recalls/abbottthoratec-corp-recalls-heartmate-ii-and-heartmate-3-left-ventricular-assist-system-lvas-due