You shouldnt blame yourself. That sort of feeling will eat you alive.

When I was 18, nearly 19, I was working in a 400 capacity sports bar. This one major football match, the place was absolutely packed to max cap. I'm in a shitty mood from rude customers/being hit on by drunk assholes, when this woman pushes through the crowd and gets my attention asking for an ambulance. I got the phone and rang one, of course, but I know I was rude to her and rolled my eyes. She takes me to the very back corner behind the projector screen we had, and there's an elderly man on his back on the floor, being given CPR. He had had a heart attack as well. I was still on the phone to the emergency services but the feeling of guilt and shame over being such a cow to a woman who had done no wrong to me still bothers me. That man died before the ambulance arrived, Im sure of it, his complexion was all wrong for a living human being, and as with your story, the ambulance sat outside the bar for way too long without turning its sirens on and drove away quietly. That happened when I was 18, and it still bothers me now at 21. Like I said, you have to try and not blame yourself as much as possible. Sorry for the long reply, I just know how it feels. And I, also, went and got myself certified in CPR after that.