Influenza immunization rates among non-elderly persons at high-risk for influenza are far below target levels in the United States. Provision of influenza vaccine at subspecialty practices can target high-risk patients, particularly during influenza vaccine shortages. We conducted a decision analysis to explore the potential effects on non-elderly cardiac patients' immunization rates of improving vaccine availability, standing orders rates, and physicians' vaccine recommendation rates in cardiology, primary care, and other medical subspecialty outpatient practices. We considered two supply circumstances (sufficient versus 50% of needed supply), and also incorporated community and hospital based vaccine delivery as well as patient acceptance in the model. With sufficient vaccine supply, optimized performance of cardiology practices (maximum vaccine availability, strong physician recommendations, and standing orders) yielded greater improvement in vaccine coverage rate than with separately optimized performance in primary care, pulmonology, or endocrinology practices. With only 50% of needed vaccine supply, reallocation of doses from community sites to primary care and cardiology, pulmonology, and endocrine offices yielded higher estimated immunization rates in the target population than strategies without reallocation. Only with simultaneous interventions across primary care, subspecialty care, inpatient, and community domains did immunization rates exceed 60%. Targeted interventions to optimize delivery of influenza vaccine in cardiology practices may be the most effective means of raising vaccine coverage levels among non-elderly cardiovascular patients, in times of varying national vaccine supply.