I've seen a lot of posts about heart worries and people who have gone to multiple doctors and still don't believe that they're OK and thought of something I saw a while back on the History Channel.
Back when NASA was sending men to the moon, they needed to rely on equipment make sure the astronauts didn't die. One example was a gauge which told them whether the air in the capsule was safe to breath or not. If it was then helmets could come off and they could breath on their own, if the gauge said it was unsafe then something went wrong and they would need to stay in their space suits or they would die.
A simple, logical theory except the known failure rate for that particular gauge was something like 1 in 250,000 meaning that for every 250,000 gauges manufactured one of them was faulty and provide a bad reading - either saying it was safe when it wasn't or saying it wasn't safe when it was. Either way, NASA didn't want to bet the lives of the men (and billions of dollars) on a gauge which could fail once every 250,000 times - the odds were too high in their opinion. So what did they do? They installed 3 of the gauges to take the same reading and decided that whatever 2 of the gauges said is the reading that they would accept because the odds of 2 out of the 3 gauges being faulty at the same time were low enough to bet the lives of the men (and billions of dollars). Essentially, they took an educated risk.
That should be the same belief we have when getting second opinions. The odds of 2 or more doctors examining you (especially when one of them in a cardiologist) and missing something are so low that its really not worth sitting there and saying "I know they missed something." Yes, it does happen, but it happens so seldom that it falls into the rare category - like winning the lottery.
The heart, while amazingly important is also amazingly simple - it acts in predictable and repetitive ways and they know what they're looking for and have tests which specially look for it and are amazingly accurate. Trust them!!!