Pumpi, they've had tests that show the heart for years. It's called an echogram. I've had them. It would be too invasive and expensive. Plus, there is no scientific evidence that shows a rapid heartbeat indicates guilt. Anyway, that's what a polygraph (also known as a lie detector machine) does. It measures the change is physiology in the human body which includes your heatbeat, bloodpressure and perspiration level. What did you think a lie detector was? There is a baseline for telling the truth which is established by asking questions. A deviation from that baseline might mean the person taking the test is lying. But it might not. (I watch a lot of detective shows.)

You wrote: "i came to the realization that lie detectors wouldn't work on all situations"
You did? I remember reading articles in the 1980s on this subject.   Pumpi, that's why since they are not admissible as evidence in a court of law. I can't say if this is a federal law or just state (someone else will have to answer that for me) A person's state of mind can alter his physical condition considerably. A sociopath can often control his response where someone who is confused might overreact.

@jxp, it varies by jurisdiction and state. If you are famous, the results may be "admitted" on the evening news (and the 'net), long before any trial.

Wanted to mention, when I said "invasive" referring to the echo, I was talking about privacy, not that the test is painful or medically invasive. (I actually had health insurance at one time - don't get me started on that subject!!) If anyone needs one, they're painless & interesting, sort of like an ultrasound. At least they proved that all those men I dated in my younger days were wrong. I DO have a heart!