Hello, welcome to Healthcaremagic. The symptom you have describes is probably related to pressure exereted by distended urinary bladder
on abdomen giving you a false feeling of pressure on heart. As night long a person doesnt go to urinate the urine formed in the night collects in bladder and gets distended and it occupies a lot more space in abdomen. But still it would be advisable to get yourself evaluated by your doctor. Wish you good health.