Background: It is already known that high coronary microvascular resistance (Rμ) is linked to altered left ventricular stiffness and might be an early indicator of heart failure with preserved ejection fraction (HFpEF). Left atrial dysfunction, on the other hand, varies according to the grade of left ventricular diastolic dysfunction. This is the first study to use the latest development for invasive assessment of Rμ and to combine it with echocardiographic assessment of left atrial strain during reservoir phase (LAS r ) by speckle tracking in relation to left ventricular (LV) diastolic function., Methods and Results: An invasive angiogram was performed in 97 patients because of suspected ANOCA. All patients underwent comprehensive echocardiography, yet image quality was poor in 15 patients leaving 82 patients to include in the final analysis. In order to compare Rμ with LAS r values, patients were divided into 4 groups based upon normal values of Rμ as defined by Fournier et al. The mean LAS r was plotted against the four resistance groups. The LAS r was 48.6% in the lowest resistance group, and 40.1%, 36.3% and 30.1% in the low intermediate, high intermediate and high resistance group respectively. These differences were significant compared to the lowest resistance group (p < 0.05). Although higher Rμ groups showed more diastolic dysfunction, LAS r was already decreased irrespective of the severity of diastolic dysfunction., Conclusion: This study shows a relationship between increased Rμ and reduced LAS r , that seems to precede conventional measures of left ventricular diastolic dysfunction. This suggests that microvascular dysfunction might be an early indicator for the development of impaired LA function., Competing Interests: Declaration of Competing Interest Nico Pijls has Institutional grant; Abbott, Hexacath. Consultant; Abbott, Opsens, General Electric. Minor equities Philips, GE, ASML, Heartflow. All others have nothing to declare., (Copyright © 2021 Elsevier B.V. All rights reserved.)