NEWARK, N.J. — A cardiologist with offices in New York and New Jersey has admitted taking part in a scheme that subjected thousands of patients to unnecessary tests and treatment and resulted in $19 million in bogus bills, what authorities call the largest case of health care fraud ever by a practitioner in either state.

Dr. Jose Katz pleaded guilty Wednesday in federal court to conspiracy to commit health care fraud.

Katz founded Cardio-Med Services LLC and Comprehensive Healthcare & Medical Services.

Prosecutors say he falsely diagnosed most of his Medicare and Medicaid patients with coronary artery disease and debilitating angina so he could treat them unnecessarily. They say he even prescribed treatment in cases in which doing so subjected the patients to risk of injury or death.

Katz is scheduled to be sentenced July 23.