After graduation, he worked for four years as a psychologist for Catholic Charities, the largest foster care and group home agency in Brooklyn, NY. For the past 35 years, he has worked in both independent practices and agency positions, including a five-year term through the Indian Health Service as the director of a large mental health system for The Cherokee Nation, a community of more than 100,000 Native Americans in Oklahoma. Upon his return to New York, Dr. Heller worked as the clinical director of a large County Mental Health Clinic that served dual-diagnosed patients. Over his career, he has diagnosed thousands of patients in outpatient settings, inpatient settings, alcohol/drug rehabilitation facilities, residential schools, and correctional facilities.