Both line-powered and battery-powered electric fences pose low risk because they are energized for a very short time — about once a second. If you accidentally touch an electric cattle fence, the momentary shock will be startling but it will not permanently damage your heart device. The shock may temporarily prevent your device from working properly, but that will go back to normal once you let go of the fence. Keep at least 12 in (30 cm) between your device and the fence power supply.