You could have a gastroscopy to find out what causes symptoms like: Low iron level Unusual bleeding Indigestion or heartburn that won’t go away with medication or returns (iron deficiency anemia) Experiencing trouble or discomfort swallowing Losing weight without trying Constantly feeling ill Black stool or blood in your stool During a gastroscopy in Mississauga, your gastroscopy doctor will take tissue samples (biopsies) and provide you with the most effective treatment.