Introduction: The most important diagnostic indicator of Acute Coronary Syndrome (ACS) is typical clinical symptoms, like chest pain, but many patients may experience nonspecific (atypical) symptoms. Understanding these symptoms and their associated factors results in early diagnosis and more appropriate treatments.

Objective: We aimed to determine atypical clinical symptoms and their predictors in patients with Acute Coronary Syndrome.

Materials and Methods: This cross-sectional study was conducted on 1167 patients with ACS hospitalized at a specialized hospital in Rasht City, Iran, between December 2019 and October 2020. The research samples were selected by a consecutive sampling method. Data were collected through a researcher-made questionnaire by interview, in which sociodemographic characteristics, risk factors, disease-related factors, and symptoms of patients with ACS were collected. Data analysis was done by descriptive statistics and multiple logistic regression by the backward LR (likelihood ratio) method. The significance level was set as P<0.05.

Results: In this study, 56.3% of the patients were male. The Mean±SD age of the patients was 60.9±11.1 years. About 28.1% of the patients experienced atypical clinical symptoms. The most common atypical symptoms were shortness of breath (29.4%), back pain (18.3%), and left shoulder pain (12.7%). The predictors of atypical symptoms were age (OR=0.98, 95% CI; 0.975 - 0.999, P=0.047), alcohol use (OR=1.86, 95% CI; 1.047 - 3.303, P=0.034), brain diseases (OR=2.36, 95% CI; 1.463 - 3.811, P=0.001), blood diseases (OR=1.45, 95% CI; 1.059 - 2.002, P=0.021), and gastroesophageal reflux (OR=1.31, 95% CI; 1.006 - 1.719, P=0.045)

Conclusion: Since more than a quarter of ACS patients have unusual symptoms, detecting these symptoms and related factors can help in early diagnosis and conduct more appropriate medical treatment.