lung function test in stress test

hey! Im 15 years old and was diagnosed with tretology of fallot when i was 7 days old, which eventually doctors realised was in fact pulmonary arteresia, i also had holes in all 4 chambers and anomolous coronary artery. This was diagnosed at great ormond street hosp. in london, when i was admitted with sats of just 27%. At 7 days old i had a stent put into my left lung artery because ultimately i was dying, i had it done to my right one at 18 months and at 4 years old i had full corrective surgery (implantation of pulmonary artery, reversing coronary artery, closure of VSD's with patches - although one was too large to close compltely) Anyhow, i was fine until i was about 8 when i was breathless, blue, lethargic etc and had to have my pulmonary artery replaced again and 2 holes repatched, luckily the surgery was performed by proffessor bonhoeffer who can now do it with a catheter which obv i was very pleased about. The surgery didnt work first time and i ended up on high dependency unit, second attempt was successful however i was in hosp for 2 weeks afterwards as the implant had severely disrupted the rhythm of my heart, i was in intermittent 1st, 2nd and 3rd degree heart block. They proposed a pacemaker but my heart prety much stopped going into 3rd degree and was mainly just in 1st so i was released without it. I was ok for a year or so until i was about 12 but i began to notice arrhythmias and was concerned but scared so i didnt tell anyone for about a year. When i did i had the usual round of tests including holter moniter for 7 days which confirmed i had 3rd degree heart block again, but the doctor also picked up atrial fibbrilation, ive never completely understood whether this is connected to the operation i had to implant the new artery? if anyone can guess let me know. Anyway i went in for an EP study and an attempted ablation of the circuits but turned out it was more complicated than expected so i was booked in for a pacemaker 2 weeks later. The op was successful but i still had something called (which i still cant spell or pronounce) wenchybach syndrome? or something.. well whatever it was it was to do with my heart rhythm so i was put on 125mg once a day of digoxin which is ok, i still get episodes and lethargy but better than before :)...i went in for a checkup a month or so ago as i was still getting episodes etc and i had a stress test, before they did the stress test i had to do the whole breathing into the mouth tubey thingy and i could only get up to 65% would that have been a lung function test? i had to breathe in loads then breath out as hard and fast as i could and push it for as long as poss, and then there was a graph on a screen that moved (i know i sound ignorant but i was so tired i was just doing what they told me to lol) anyway yeh they said my best was 65% if thats a lung function test isnt that not great? if so whats the risks? should i ask about that next time i go? its concering me as i do still get out of breath but with my condition i suppose its expected.

sorry about the long medical history lol - i thought i might help to answer the question.

thankyou!!! Georgia