That burning sensation in your throat and chest has nothing to do with your heart and everything to do with your stomach. Pregnancy hormones are largely responsible for the heartburn that plagues many expectant moms. The hormones relax the muscles between the stomach and the esophagus, which allows stomach acids to back up and irritate your system. Indigestion is a different problem- it happens when a sluggish stomach (slowed down, again, by those "relaxing" pregnancy hormones) takes too long to empty itself, making you feel gassy, bloated, and overstuffed. Both heartburn and indigestion often appear during the second trimester and can worsen as the growing uterus presses up against the stomach, giving it less room to do its job.