The fear of having a heart attack increases the intense of panic attack because of fear. Especially during the first onset of panic attack. Most people think they are having a heart attack than to think it is only a panic attack. Many knows what is heart attack than panic attack.
Hold tightly in your mind that there's nothing serious about panic attack. No one dies due to panic attack so, there's nothing to worry. It's your fear that triggers the episode of panic attack. Avoid and you have to get rid of it.
Heart attack is physiological while panic attack is psychological. It's the heart that causes heart attack while in panic attack it's the mind! To give you a peace of mind consult your physician and run a laboratory test. If all test resulted to negative outcome, be happy. It's only a panic attack. You can overcome it through your mind onset.