I get the tachycardia, but was told it was common. I've been to the hospital a couple times for heart related problems due to things other than MJ. I still get the racing heart beat from time to time, and like birdgirl said, the sativa strains make it worse, which is why I smoke indica nowdays.

Most of my problem is due to panic, and anxiety, as they have found nothing wrong with my heart yet. It's scary when it happens, but for me, it only lasts between 30 mins to an hour.

I just try to stay calm, and relaxed and that seems to help, too.