Dr. Gremmels is a native of Lisbon, North Dakota. After receiving a Bachelor of Science in Genetics and Cell Biology from the University of Minnesota he completed Medical School at the University of Chicago. Dr. Gremmels completed a pediatric residency and Chief Residency at the University of Colorado, Denver Children's Hospital. His fellowship in Pediatric Cardiology was completed at the Department of Pediatrics at the University of California San Francisco Medical Center. Dr. Gremmels then joined the Children's Heart Clinic in 2003.

Dr. Gremmels is board certified in pediatrics and pediatric cardiology. He is a member of the American Academy of Pediatrics, the American College of Cardiology and the American Heart Association. He also serves as a Director of Echocardiography at Children's Hospitals and Clinics and is a member of several committees.

Special clinical interests include echocardiography, fetal echocardiography and cardiac intensive care as well as all aspects of general pediatric cardiology.

Dr. Gremmels, his wife and daughter live in Minneapolis.