No doubt about it -these are horror stories. There's the 13-inch metal tool left in a patient's body, the women who underwent heart surgery scheduled for a different patient, and several cases of surgery on the wrong side of the body. Pictured is Jésica Santillán, who died after a heart transplant from a donor with an incompatible blood type.
The error sent the patient into a comalike state, and she died shortly after an attempt to switch the organs back out for compatible ones failed. The hospital blamed human error for the death, along with a lack of safeguards to ensure a compatible transplant.
Link
That should tell you how often mistakes are made.... it's very scary.