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If you have a feeling of heart stopping with heaviness in chest then it may be due to :-
-heart problem like ischaemia (reduced blood supply to heart);heart block
and mental stress
Please visit a ER or a hospital and get a ECG done to rule out heart problem.If the ECG shows any changes due to heart problems they will start treatment and if the ECG is normal and you have this problem due to anxiety then the doctor will prescribe you anxiolytic.