To anybody concerned about their blood pressure, don't underestimate the effect of weight loss on same.
March 2012 saw my BMI at 28, blood pressure 140/95. This was for an aviation class 1 medical renewal. The medical examiner passed me (most medical exams take into account 'white count syndrome' having some effect on your blood pressure on the day) but recommended, even though I wasn't 'fat', losing weight as it had worked for his higher than average blood pressure.
These days my BMI is circa 21, blood pressure a perfect 120/80. I've done nothing else to help reduce it, just improved/reduced my diet over the past 18 months and my blood pressure has reduced accordingly.
This is also helpful for a healthy heart. The basic principle of an ECG is to pass a small electric current through your heart and upper torso, the idea being that if the current shows any 'discontinuities', it could indicate tissue damage resulting from a heart attack/disease etc. Obviously such tissue will have a different electric conductivity than healthy tissue.
When I queried common failing points to my medical examiner, his reply concurred with TDK's response above - blood pressure is by far the most common failing point, followed by unhealthy BMI, with things like colour blindness and heart problems generally being quite rare, but picked up because the candidate hasn't been examined in this way recently, and most probably wasn't even aware of any issues.
Ironically, I was that worried about the ECG (fear of the unknown), it took us a good ten minutes of ECG printouts until my heart rate was considered acceptable. I'm not sure if BUPA (or the respective TOCs) accept this, but I believe that to cater for those who suffer badly with white coat syndrome, some examinations require the candidate to wear a 24 hour heart monitor to confirm whether it is just down to nerves, or if the high rate is actually an issue.
Either way, every medical I have attended has never been as bad as I thought it would be, so it's best not to think about it to much... For your heart rate's sake!