Abstract CORRELATION OF NITRIC OXIDE AND GENDER ON CORONARY SLOW FLOW PHENOMENON OF CORONARY HEART DISEASE PATIENTS Background Coronary Slow Flow Phenomenon (CSFP) elucidate the delayed progression of the injected contrast medium through the coronary arteries during angiography without obstruction of the epicardial coronary arteries. Nitric oxide (NO) as a vasodilator substance that normally found in all blood vessels that may trigger the CSFP. Objective To determine the correlation of Nitric Oxide (NO) levels of Coronary Heart Disease patients accompanied by Coronary Slow Flow Phenomenon (CSFP) based on gender. Method This research is an analytical study with cross sectional design. The study was conducted at dr. Zainoel Abidin hospital Banda Aceh, yet, the data was collected by studying the medical records of patients undergoing coronary angiography from January 2019 to July 2019. Assessing levels of Nitric Oxide based on patients’ gender with Coronary Slow Flow Phenomenon using Lilliefors (Shapiro-Wilk) normality test, Chi square test or Fisher, the T-test, and the Kruskall-Wallis test with Mann-Whitney. Results The subjects of this research are 30 patients which are divided into 2 groups based on gender with a ratio of male and female is 1:1. The result of this study shows the differences of Nitric Oxide levels of Coronary Slow Flow Phenomenon patients based on their gender, the females are higher than males with an average of 50.92 ± 20.37 µmol / L and 31.57 ± 10.58 µmol / L respectively. The statistical analysis with the Spearman test shows that the level of Nitric Oxide is inversely proportional to the number of frames (negative correlation). Conclusion: There are differences in levels of Nitric Oxide (NO) between female and male patients that suffered coronary heart disease accompanied by CSFP which are statistically significant. Keywords: CSFP, Gender, Nitric Oxide