The pilot refueled the Piper Cub and took off without mishap. The pilot was engaged in patrolling pipelines, and during this portion of the westbound route over 8,000 foot mountainous terrain he was positioning the airplane between segments. There were no witnesses to the crash and the pilot did not establish contact with ATC. The airplane crashed about 9 miles west of the departure airport. The airplane was found in a near vertical attitude, heading east, and with its engine about 4 feet beneath ground level. Exam of the airframe and engine revealed continuity of the flight control system, fuel in the engine and no evidence of any preimpact mechanical failures. Medical records indicated the pilot had experienced a pain in his chest. Family members reported that the pilot had recently experienced chest pains which were severe enough to result in the pilot interrupting his activity. During the autopsy the pathologist performed a microscopic exam of the heart and found nuclear pleomorphism and hyperchromatism. No acute changes were present.