My son got this suddenly when he was 21 years old and he's had it ever since. They never worked out why he had it but his heart was fine. It all started out when he was training to go into the army and he had to run so many miles so he ran and ran and ran until he almost conked out one day and then the tachy cardio wouldn't go away. He constantly lived with it everyday so he had to go and see a doctor. He still gets it on and off today but he's not on medication.