Hi welcome to HCM For your info , Exercise and physical activity can generate palpitations, as can anxiety or stress. As you say , Your heart seems to be beating hard, although not really faster, when you are at rest , feel no pain , means ,you have nothing to worry much . Weightlifting due to the muscular exertion delivers an increased return of blood to the heart due to the pumping effect of skeletal muscle, can cause palpitation . Avoiding factors like , Stress, anxiety, or panic , dehydration , low potassium , low blood sugar , too much caffeine, chocolate, or alcohol , nicotine , vigorous exercise , fever , anemia , and including diet containing essential nutrients will help you feel normal , Most palpitations are caused by a harmless hiccup in the heart s rhythm. A few reflect a problem in the heart or elsewhere in the body.. Whenever you feel so , take rest for some time . Take deep breaths slowly . Occasional check ups from your your doctor is advisable . Hope this helps solve your query Take care All the best. wish you good health ahead