What Causes Rapid Heart Rate Along With Severe Acid Reflux?

My step-father has been struggling with a very fast heart rate and what seems like GERD or acid reflux. He had an upper GI done, and also ended up with a pacemaker (for tachycardia). Tonite, his resting pulse was 190, and he was having severe acid reflux symptoms such as gas, etc. He is on his way to the hospital with my sister and mother. Could hiatal hernia be overlooked with an upper GI, or would it show definitively. What else could this be? The reflux-like symptoms have been bothering him for quite a while...