Atrial fibrillation (AF) is the commonest condition affecting the rhythm of the heart and causes an irregular and often rapid heartbeat. Developing this condition may cause significant health problems and symptoms that affect normal day-to-day activities. Patients with AF also have a shorter life expectancy on average. Tablets used to try to normalise the heart rhythm rarely work well. As a result, doctors have devised a treatment to try to cure this condition. Special wires (called catheters) are used to deliver heat energy (called ablation) on the inside surface of the heart. This technique has been used more and more in recent years for patients with troublesome symptoms due to AF.

The aim of the treatment is to draw lines of ablation in specific places in the heart. Unfortunately, a lot of patients (almost 50%) get AF again after this treatment and most of these patients have a second treatment performed. It is usually found at this second treatment that gaps have developed in the lines of ablation that were drawn the first time around. The investigators think that electively doing a second treatment to close these gaps a couple of months after the first treatment may mean that fewer of these patients will get AF again in the future. The investigators also want to find out what factors make a line of ablation less likely to develop gaps.

In this study, participants will be assigned to one of two groups:

1. a "standard care" group, who will have a single treatment initially.
2. a "repeat study" group, who will have the initial treatment followed by a second treatment 8-10 weeks later.

For patients in the "repeat study group", investigators will see how many have developed gaps since their first treatment. The investigators will look at where these gaps are and will compare this with information collected during the first treatment to try to work out why the gap has developed. Any gaps found at the second treatment will be closed again.

All participants will then be monitored carefully over 12 months to see how many from each group get AF again. To do this, all participants will be given a handheld heart rhythm monitor to keep until the end of the study. This device is simple to use. Participants will be asked to make a 30 second recording of their heart rhythm each day and also whenever they have symptoms. These recordings will be downloaded at review appointments arranged 6 weeks, 3 months, 6 months and 12 months after the initial ablation procedure.

Inclusion Criteria:

• Aged over 18 years
• Current pattern of paroxysmal AF (defined as electrocardiogram (ECG)-proven episodes of AF which are self-limiting and last less than 7 days on each occasion, or which were cardioverted electrically or pharmacologically less than 48 hours from onset)
• Due to undergo pulmonary vein isolation by radiofrequency (RF) ablation

Exclusion Criteria:

• Inability or unwillingness to receive oral anticoagulation with warfarin or alternative anticoagulant drug
• Previous ablation procedure for AF
• Unwillingness or inability to complete the required follow-up arrangements
• Current pattern of persistent (episodes of AF which last longer than 7 days or which last longer than 48 hours but require electrical or pharmacological cardioversion) or permanent AF
• Prior prosthetic mitral valve replacement or severe structural cardiac abnormality
• Reversible cause for AF
• Known infiltrative cardiomyopathy
• Known severe left ventricular systolic function (ejection fraction <35%)
• Pregnancy