Abstract Background: Dysfunction of the coronary microcirculation may be one of the factors responsible for persistent anginal symptoms. Noninvasive as well as invasive modes for assessing microcirculation have yielded inconsistent results. Aim of work: To determine the usefulness of coronary sinus filling time (CSFT) for assessment of microcirculatory transit time in the coronary circulation. Subjects and methods: A case-control study carried out in the Cardiology Department, Zagazig University Hospital on 57 patients divided into three groups: Group A included diabetics with angina, Group B included non-diabetics with angina, and Group C included control group. All patients were subjected to complete history taking, general examination and local cardiac examination. 12 Lead ECG, stress ECG (treadmill test), transthoracic echocardiography and coronary angiography were done. Results: regarding CSFT in group A the mean was 5.247 ± 0.562, in group B the mean was 4.635 ± 0.224 sec and in group C the mean was 3.295 ± 0.525 sec. There were significant difference between group A and control group (P < 0.001), between group B and control group (P < 0.001) and between group A and group B (P < 0.001). There were statistically significant relation between prolongation of coronary sinus filling time and presence of comorbid hypertension (P < 0.001), dyslipidemia (P < 0.05), Family History of CAD (P < 0.001) and obesity (P < 0.05). Conclusion: The coronary sinus filling time is a useful method for assessment of microcirculatory transit time in the coronary circulation. The prolongation of coronary sinus filling time is significantly associated with the presence of diabetes mellitus.