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Johannes Karl Martensson, M.D., Ph.D.

Johannes Karl Martensson obtained his MD at the University Medical School in Uppsala and Linkoping and his PhD (in Biochemistry) at Linkoping University Medical School, in Sweden. He came to the USA as a Visiting Professor in Biochemistry at Cornell University Medical Collage, New York, in 1986. He was promoted to Associate Professor in Biochemistry and has 58 full-length publications, including 8 publications in the Proceeding of National Academy of Sciences on the importance of glutathione and vitamin C in anti-oxidant defenses, mitochondrial function and cell death.


He completed his Internal Medicine Residency at Greenwich Hospital/Yale University Medical School and his Gastroenterology Fellowship at Thomas Jefferson University Hospital and Pennsylvania Hospital, Philadelphia.


He moved to Citrus County in 1996 to join Citrus Gastroenterology and Fernando Bueno MD. He continues to enjoy working in this vibrant community, full of challenging medical conditions and patients in need. He has a specific interest in risk factors of cancer development and treatment, inflammatory bowel disease, bile duct and liver diseases, inflammatory conditions related to GERD and Esophageal cancer and functional disorders related to previous gastro-intestinal surgery. He is an advocate for preventive medicine and enjoys many of the outdoor activities found in this beautiful part of Florida. He is part-owner in Suncoast Endoscopy, Inverness, an efficient out-patient surgical center, and he is on staff at both Citrus Memorial Hospital and Seven River Regional Medical Center.

View Curriculum Vitae (CV) Here
Agda Hart PA-C

Agda completed her undergraduate degree at Cornell University in Ithaca, NY and her PA degree at Baylor College of Medicine in Houston, Texas. She has been a practicing PA for over 35 years. She has maintained certification with the NCCPA over her entire career. She had been employed with Citrus GI since July of 2016.

She has always been an advocate of preventive medicine through out her career. In her first job as a PA, she worked in Radiation Oncology with several colorectal cancer specialists. She saw many people who were diagnosed with colorectal cancers in the days before colonoscopy was available for prevention. She feels it is especially rewarding now, to be evaluating patients and ordering endoscopic procedures that can be lifesaving. It is particularly gratifying because, in the early days of her career, her job encompassed implementing treatment plans to help patients survive advanced colorectal cancers many that can now be prevented by effective endoscopic screening. There are many noncancerous GI diseases which cause life altering discomfort. Agda feels it is a privilege to be in an occupation where her mission is to care for people. It is very rewarding to work on a team where complex diseases are diagnosed and to be able to formulate treatment plans that promote recover. She feels that being involved in helping patients to feel better is the most rewarding experience that a health care provider can experience.

Agda and her husband and family moved to Florida in 2004. She is a mother to three and a grandmother to six and enjoys sharing time with her family. She is known for her love of pets and enjoys gardening and crafts of all types where she can express her creative side. Agda loves to travel and interact with people across the world . She has traveled extensively in the US, and has been across Europe, to Sweden, China, Japan, Turkey, and Iran, Mexico and the Caribbean.

Our Office Staff

Here at Citrus Gastroenterology, PA, our entire staff believes excellent medical care is about heartfelt caring and compassion. That is why you’ll feel comfortable from the moment you walk in. You’ll appreciate a staff who knows you by name and doctors who treat you like family.

Citrus Gastroenterology, PA accepts most major insurance plans. Please call our Main (Inverness) office at 352.344.8080 for more details or to schedule an appointment. We look forward to helping you live a happier, healthier life.