A woman who was called lazy because she fainted during exercise is recovering after an operation to repair a hole in her heart that was described by cardiologists as one of the biggest they had seen.

Despite Louise Banks’s suspicions that she might be suffering from a heart problem – which appeared to worsen dramatically when she tried to exercise – doctors repeatedly misdiagnosed her condition throughout her teenage years.

Ms Banks, now 23, even resorted to joining a gym to prove that she was not lazy, as her school PE teacher claimed. While running on the treadmill she discovered that her heart rate went down instead of up.

However, it was only this January, seven years later, that her condition was finally identified after a new GP recorded an irregular heartbeat during a 24-hour monitoring test.

The scan revealed a tear 4cm (1½in) long in the partition between the right and left side of her heart that enlarged when more blood was being pumped through. The result was lack of oxygen in the blood reaching her brain, causing her to faint.

The condition could have killed her at any time in the previous 23 years.

Heart surgeons at Southampton General Hospital have now repaired the gap. She has been left with no lasting effects apart from a 25cm scar on her chest and a temporarily enlarged right side of the heart. Ms Banks is now back at her home in Exeter, Devon, with her partner Matthew Folland, 30, and their son Ben, 4, and is looking forward to catching up on all the things that she could not enjoy as a teenager, including sports and dancing.

She said: “I always knew there was something wrong because I could feel my heart start and stop like a baby wriggling in my chest. I’m looking forward to my new life. It will be great to be able to dance with my friends without collapsing.”

At the age of 8 she was described as a “fainty child” after passing out at school. When it happened again she was told that she was epileptic.

At 14 she complained of having palpitations up to 70 times a day. At 16, fed up with the taunts, she joined a gym.

Her condition was once again misdiagnosed when she complained that her heart rate was falling instead of rising as she tried to work up a sweat.

When she was 19 she almost died in childbirth when her heart started fluttering.

An ultrasound test revealed an atrial septal defect, or hole in the heart, between the two main chambers, or atria.

Cathy Ross, a senior cardiac nurse with the British Heart Foundation, said that a hole in the heart just 9mm long was considered large and Ms Banks’s was more than four times that size.

Mrs Ross said: “She is incredibly lucky. I’ve never heard of anyone having a hole in their heart that large.”

Ms Banks does not harbour any grudges against the doctors who misdiagnosed her condition.

She said: “I don’t feel angry with the doctors for missing it. I would rather have been operated on now than 23 years ago when science wasn’t so advanced.”

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