Nowadays my heart beats hard like really hard on being fast or really slow.usually while playing games.my face too changes from any expression to a really upset and uncomfortable face when that starts happening.usually when i am shook.what is this?

This is called anxiety. There are real changes in chemicals/hormones/neurotransmitters that occur in these situations. These changes can absolutely lead to the symptoms you describe. There are many ways to overcome these physiologic changes, such as deep breathing, meditation 🧘‍♀️, even medications 💊can be used if severe enough. Talk to your doctor about referral to behavioral psychologist.