Take it easy
Your ticker is working overtime during pregnancy, pumping more blood through your body, and your lung capacity is decreased now too, which means you'll have a harder time catching your breath. That's why some doctors recommend you keep your target heart rate at 140 beats per minute or less. But an easier way to know if you're exerting yourself too much is simply make sure you can breathe normally. Some sweating and breathlessness is OK, but if you find yourself constantly winded or heart pounding, you should ease up a bit. Stop exercising when you feel fatigued and don't exercise to exhaustion.