Are ecg machines more accurate when exercising? i'm talking about a mobile portable type. in other words. is it better to measure the heart when its in a resting state or when its working harder when looking for issues?

This is a confusing post. The EKG machine is as accurate as it will be in any setting. There is value in a "stress test" where the same machine is applied the same way while the patient walks on a treadmill to bring up the heart rate to reflect a more demanding physical setting. The extra stress can bring out more information about heart function.