At 18 I went for my class 1 renewal and was told I had a murmur. Obviously it had been missed a year earlier for my initial with the same doctor. Unlike veetwo, I was sent for an ECG and echocardiogram, possibly because my blood pressure was through the roof. (something like 160/120). I wore a blood pressure monitor for 24 hours and the average ended up being 112/78.
I was cleared after all these tests, and the doctor thought white coat syndrome was the cause of my blood pressure spike. As far as renewals go, I have not had any murmur issues since, and if my blood pressure is high, the Doc makes a nurse sit with me and retest it until it goes down. This was only the case for the following year, and I have had no issues since.
I also had a foreign class 1 issued, and the docs got wind of my history as they required previous reports from Aus. Once I showed them the specialist reports (which I took with me) no further questions were asked and I was not subjected to any further tests.