What cardio do you do while preg?

I like to run for exercise and was told at my 1st prenatal appt that I need to keep my heart rate between 120-140 in order for exercise to be safe. That pretty much throws my any running out of the window and would limit me to brisk walking. I do have a HR monitor so I know where I'm at... Any suggestions?

I did spinning during both my pregnancies.  I was told the 140 rule too, but I wore a heart rate monitor and jus****ched it go much higher than that all the time.  I'm no doctor, but I think how you feel is a much better indicator of how you're doing than an arbitrary number.  If it is exercise you're used to doing, I say keep doing it.  Just make sure to drink lots and stop if you ever feel lightheaded, dizzy, too hot, or even just "off".  But, again I'm not a doctor.