So, the DH is doing fine, all things considered. Our luck was amazing; things couldn't have fallen together any better. The EMTs were there within minutes of our call, and their tests didn't show anything to worry about. DH opted to go down to the Cardio ER anyway for further checks. The tests there only showed one slightly abnormal result, but the ER Doc decided that they should start the more invasive test... which showed a major blockage. The blockage was being cleared within 4 hours and prognostication for heart muscle recovery is optimistic.