The Ontario Government (Canada) has contracted EMS helicopters for more than 35 years and have not (hopefully never) had patient or pilot killed in that time. They presently operate 11 S76 aircraft with 2 crew.
They have contracted Bell 212 aircraft in the past and have ordered 10-12 AW139 to commence operations in 2010. For the most part they operate in very remote areas with few facilities, their secret is 2 IFR rated pilots on all operations, simulator training and sticking to the regulations.
They did have an accident in December 2007. No patient on board- some serious injuries to the crew though.
On the fixed wing side they have had a couple of serious ones with fatalities.