Mechanical. It was rated to last much longer than the pig valve.
On a humorous side note, the mechanical one audibly 'ticked' when her heart rate went up. We teased her about never being able to sneak up on us again.
31 posted on 10/23/2011 4:13:52 AM PDT by MamaTexan
(I am ~Person~ as created by the Law of Nature, not a 'person' as created by the laws of Man)