I had a similar issue. Chest pain that eventually drove me to the ER. Negative cardiac results - I didn't have a cath - I had a coronary artery CT arteriogram. I have stellar coronaries. However, I have a history of gastric reflux and the best guest was I had referred chest pain from esophagus spasms. Apparently the phrenic nerve can become involved in the spasm & that can radiate the pain to the left chest & shoulder. I haven't had any recurrences since they changed up my reflux medication.

If you're concerned about activity impacting your heart - I have noticed my Fitbit has an option to monitor for arrhythmias. It's on the premium package - but its a small price to pay to be able to keep an eye on one's heart in real time.