ABSTRACT BACKGROUND: Diastolic function has been reported to be impaired in many patients with coronary slow flow phenomenon (CSFP). CSFP has broad spectrum of clinical presentations, including non-ST elevation myocardial infarction (NSTEMI). We sought to study the shortterm evolution of diastolic function in CSFP patients presenting with NSTEMI. METHODS: This study included 92 patients with CSFP and acute NSTEMI. Conventional echocardiography Doppler imaging and tissue Doppler echocardiography imaging were used to evaluate diastolic function during index NSTEMI and after 3 months. RESULTS: Mean age of study patients was 45.7 ± 6.8 years. The prevalence of diastolic dysfunction (DD) at baseline was 69 patients (75%) and 28 patients (30.4%) at 3 months, p < 0.001. Various diastolic function indices showed significant improvement from baseline to 3 months follow-up. E/Em was 17.32 ± 3.41 at baseline compared to 12.41 ± 5.58 at 3 months, p = 0.039. Septal e′ velocity was 5.67 ± 4.56 cm/s at baseline compared to 7.78 ± 3.22 cm/s at 3 months, p = 0.023. Medications used were not significantly different between those with improved versus unimproved DD. CONCLUSIONS: Diastolic function seems to improve over short-term follow-up in patients with CSFP presenting with NSTEMI. This could reflect a transient worsening during acute NSTEMI. Keywords: Coronary slow flow; Non-ST elevation myocardial infarction; Microvascular dysfunction; Diastolic dysfunction