Normal young people often have premature beats when they take a deep breath, which is normal. If it has nothing to do with strenuous activities, there is nothing to do. As for joining the army, if you can't do an electrocardiogram, it proves that you are fine. Of course, you can join the army. But if you detect an ECG, it means that your premature beats are a little frequent, because the ECG was only taken for a short time. All suggestions should be checked in the hospital, don't worry. Good luck.