Objectives To determine the rate and nature of complaints and the outcomes of the complaint management at a large heart centre in Tehran. Results A total of 1642 (5.2 per 1000) complaints were received, of which 1457 (4.64 per 1000) were verbal, and 185 (0.56 per 1000) were in written format. 34.7% of the complaints were related to admission procedures, followed by 34.1% communication, 13.8% waiting time, 6.8% delay and 4.1% ignoring the standards of clinical care. Over 90% of complaints were resolved by explanation or verbal apology, 2.1% of them led to a change in the process or procedure, and 4.8% were deemed disapproved claims. Conclusions The majority of patient complaints in Tehran Heart Centre are related to admission procedures or communication; most of them are verbal and resolved in the early stage as an explanation or apology. The hospital complaint management system has the potential to resolve the majority of such complaints in an early stage.