What causes heart pain when you use the restroom?

Valsalva?: Straining to have a bowel movement creates the valsalva maneuver, which can dramatically lower the heart rate. This can cause several problems, including fainting.

Needs evaluation: Any exertional chest pain merits evaluation to make sure it's not due to coronary artery disease. This requires a careful history and physical exam by your physician to determine whether or not further testing is needed to answer the question.

Confusion: There is nothing about using the restroom to cause heart pain. If you have pain from your heart (aka "angina"), it will occur with any form of exertion. Pain in your chest with valsalva ("pushing", like with a bm) can be due to acid reflux and is the more likely cause of your chest pain.