Horrible idea...
As an emergency medical technician (EMT) one of the most common types of patients I encounter is the cardiac emergency. We are especially alert of patients with "ST elevation" in their EKG, which indicates a specific kind of heart attack. I can only imagine that a new onset ST elevation wouldn't allow a user to access his or her phone if it were locked by EKG shape. I'm sure the courts would have a field day with a product liability case where somebody couldn't unlock their phone to call for help because the phone didn't recognize their heart beat shape.