What Causes Prolonged Palpitations?

My 7 year old grand son told me his heart is beating hard and fast ( he was sitting at my laptop, looking at shoes online! ...nothing exciting!); I didn t check his rate, but it was beating hard. ( I have the same thing about twice a year - for the past few years- but I am almost 70!) . it lasted about 1 hour. Is it something to worry about? Thank you!