It seems like the first doctor gave you the diagnosis of suspected hypertrophic cardiomyopathy. It's actually not really that uncommon and it is an illness very different to what gives you classic "heart attacks". It comes from heart walls being thickened, oftentimes from dealing from long term high blood pressure or just bad luck with genetics.

It comes in two forms mainly, one where blood can pass easily, and one where it has to struggle a bit. But it seems like the diagnosis was actually not made, but a guess that this could be behind your issues. You probably have the right to a printout of all your tests and records to see what was actually found out.

Symptoms can be irregular heart beats and palpitations. If you have this, the main thing to do is getting blood pressure down and heart rhythm stabilized. I assume you will go on checkups to see that the med you are on (I don't know much about it), actually deals with heart rhythm because if you indeed do have this, it is important that your heart ticks on as stable as possible. The treatment options are somewhat limited.

Maybe the other doctor just wants to calm you if you are already treated the best way possible?