According to Deputy Greg Genz from the Elmore County Sheriff's Department, the man was fishing with friends at the local reservoir when he suddenly collapsed in the boat around 11:45 a.m.
His friends started to administer CPR as they drove their boat to the nearest docks and continued their efforts for approximately 10 more minutes until an ambulance crew from Grand View arrived on scene.
Despite their life-saving efforts, medics at the scene were unable to revive the victim and was declared dead approximately an hour after he suffered the heart attack, Genz said.
The individual's name was withheld by the county sheriff's department pending notification of his next of kin.

Comments
I know the USAF Marina has CPR/First-aid trained personnel working there and they have an AED available. I believe it is the only one in the area for cases like this, 10 minutes is a long time even with CPR.