Cardio Exercise Exhaustion

39yr old male (40 in 3 months), 5 "10, 185lbs, overall good health, family history of high blood pressure (mine is fine), mom and both brothers on med. and stroke(s), uncle, mom, grandmother  any cardio exercise has always been difficult for me, recently (6wks) I been doing BIKRAM Yoga 3x per week, after struggling in every class, I wore my heart rate monitor and noticied my heart rate quickly gets in the 180's and averages > 140 through out the 90 minute class, even with my numerous long breaks.... I get physically exhausted quickly, heart feels like it is going to explode, heart rate stays high 80-90's hours after class, I fell completely spent and physically exhausted after....   am I just really out of shape or is something else going on....  even when I take a break in class, I can't seem to "recover"  today was horrible, I stay very hydrated throughout the day........  would an exercise stress test be advisable for peace of mind?

[peekawho]

You should see your doctor.  

I had a similar onset of problems and have pulmonary hypertension.  Not that this is what's wrong with you, but its always advisable to see your doctor if you are having exercise intolerance, shortness of breath, and severe tachycardia.