Executive Officers

Taejoon Ahn, MD MPH CPE
President & Chief Executive Officer

Taejoon Ahn, M.D. became the president of John Muir Medical Group (JMMG) in January of 2014. He leads a medical group of over 350 clinicians, mostly in primary care. JMMG is the exclusive contracted provider of primary care services for John Muir Health, partnering closely for over 25 years. Prior to the presidency, Dr. Ahn served as vice president and medical director of urgent care services for JMMG. He also worked as faculty for the University of California, San Francisco's National HIV/AIDS Clinicians' Consultation Center. He is currently an Assistant Clinical Professor of Family & Community Medicine for UCSF.

Dr. Ahn has also served as director on the board of John Muir Health and is currently serving as Director on the board of Canopy Health. Canopy Health is a joint venture between multiple provider groups to offer a large network in the San Francisco Bay Region.

Dr. Ahn is the current Chair of the Medical Practice Affairs Committee for the California Academy of Family Physicians and also serves on the CAFP Audit/Compliance Committee. He has also served on CAFP’s Board of Directors, Legislative Affairs Committee as Chair and for the California Medical Association’s specialty delegation and council on legislation.

Dr. Ahn received his medical degree from the University of California San Francisco, where he also completed a residency in Family & Community Medicine. He received his Masters in Public Health with an emphasis in Epidemiology from UC Berkeley. He is an alumnus of the California Healthcare Foundation's Leadership Fellowship and is a certified physician executive with the American Association for Physician Leadership (formerly the American College of Physician Executives).

Ravi Hundal, MD
Chief Financial Officer and Executive Vice President of Clinical Integration & Population Health

Ravi Hundal, MD is an accomplished family physician with over 25 years of experience in the health care industry. Dr. Hundal is currently the Chief Financial Officer and Executive Vice President of Clinical Integration John Muir Medical Group (JMMG) an organization with 350 plus physicians. As the CFO/EVP Dr. Hundal is primarily responsible for managing the company’s finances, including financial planning, management of financial risks, and financial reporting. Dr. Hundal also sits on the following boards, John Muir Health from 2013 to current, America’s Physicians Group a national medical group organization, and he chairs the John Muir Health Clinically Integrated Network/ACO Board.

His previous executive positions include, JMMG voting board member from 1999-2010, Board member of John Muir Physicians Network from 2009 to 2013, and Board member of Seven Hills School from 1999 to 2005.

Dr. Hundal received his medical degree from Autonomous University of Guadalajara, and completed his family medicine residency at Contra Costa Regional Medical Center in Martinez, CA. He also received his bachelor’s degree in Biology from the University of California Davis.

In his spare time Dr. Hundal enjoys wine, food, and traveling with his wife Dr. Marie McGlynn and spending time with his family. He also enjoys various sports including lacrosse, soccer, and hockey.

Tanya Threewitt, MD
Chief Operating Officer and Senior Vice President

Tanya Threewitt, M.D. joined John Muir Medical Group in 2002 and has dedicated 23 years of progressive experience to the Group. She became Chief Operating Officer and Senior Vice President in May 2026. Her primary role is to lead operational strategy and execution, overseeing all aspects of ambulatory and hospitalist operations, ensuring clinical excellence, financial sustainability, and alignment with the group’s mission to improve community health.

In January of 2023, Dr. Threewitt began serving as Vice President of Ambulatory Health, overseeing operations at 29 primary care practices, managing 175 clinicians and seven direct reports. She was heavily engaged in long-term planning for ambulatory health specialties, ensuring alignment with the health system strategy. She executed initiatives to provide more effective, efficient care that improved patient health while lowering overall healthcare costs. She led organization-wide process improvement initiatives applying Lean Six Sigma methodologies to define problems, streamline workflows, and drive measurable success. She advanced team-based care models by strengthening collaboration between physicians, nurse practitioners, and physician assistants, building trust, addressing liability concerns, and expanding NPs/PAs into primary care clinics.

As Executive Medical Director of Ambulatory Operations from (Apr 2017 – Dec 2022), Dr. Threewitt oversaw 35 primary care and five urgent care practices with 11 direct reports. She developed strategic plans for urgent care, pediatrics, family medicine, and internal medicine. She managed budgets to reduce costs and allocated resources for staffing and clinic needs.

From (Jan 2015 to Mar 2017) as Medical Director of Ambulatory Operations and Family Medicine, Dr. Threewitt oversaw 35 primary care clinics, addressing compliance issues, onboarding new hires, and managing call pools and float coverage. She standardized clinical workflows across all sites and developed strategic initiatives to increase patient volumes and support sustainable business growth.

Dr. Threewitt was Associate Medical Director of Family Medicine from (Jan 2014 – Jan 2015) and served as an SME for all family medicine related matters. From (Jan 2008 to Jan 2014) she served as Associate Medical Director of Information Technology and successfully implemented CernerEHR, followed by a transition to Epic EHR, enhancing health record management and clinical interoperability. She served as a strategic advisor to IT teams, providing physician-level insight to optimize usability and workflow integration.

Dr. Threewitt currently sits on the John Muir Health Value Based Care Council and the John Muir Health Strategic Planning and Marketing Committee.  From 2013 – 2018 she served as co-chair of the Physician Strategic Council. She sat on the Board of Directors for John Muir Medical Group from 2011 – 2021, serving as Board Vice Chair from 2014 – 2021.

Dr. Threewitt holds Lean Six Sigma Certification (Yellow Belt) from Lean Six Sigma Institute. She completed a Fellowship inHealthcare Leadership, from the California Healthcare Foundation

Born and raised in San Jose, California, Dr. Threewitt received an undergraduate degree in psychology from UC Davis. She graduated from Hahnemann Medical School in Philadelphia and completed her Family Medicine residency through UC Davis in Modesto, California at the Stanislaus County Doctor’s Medical Center.

Dr. Threewitt lives in Clayton, CA with her husband and enjoys travel, live theater and all things Science Fiction/Fantasy.