Anxiety is one of the main causes of heart attacks in patients hospitalized for heart disease. There are different ways to reduced anxiety. Aromatherapy is one of the methods used to reduce anxiety. This study determines the effects of aromatherapy on anxiety of patients with ACS hospitalized in a cardiac care unit. This clinical trial was conducted in 2016 on 60 patients diagnosed with ACS and hospitalized in CCU of 22 Bahman Hospital, Gonabad. Patients were recruited by convenient sampling and assigned randomly to control and experiment groups. The experiment group received aromatherapy with a combination of essential oils of lavender, Matricaria recutita, and neroli (6:2:0.5) three consecutive nights; the control group received no intervention. Data were analyzed by using SPSS20, independent t-tests, chi-square test, and exact Fisher test (p < 0.05). Each group contained 30 participants who were not significantly different in terms of underlying characteristics (p > 0.05). There was a significant difference in the mean score of anxiety post- (p < 0.04) and pre-intervention (p < 0.001). The post- and pre-intervention scores were significant between the two groups (p < 0.001). The mean score of anxiety increased in the control group and decreased in the experiment group. Thus, it was concluded that aromatherapy is a cost-effective and uncomplicated method that can reduce anxiety of patients with ACS hospitalized in the CCU.