Micro-vascular flow in the myocardium is of significant importance clinically but remains poorly understood. Up to 25% of patients with symptoms of coronary heart diseases have no obstructive coronary arteries and have suspected
microvascular diseases. However, such microvasculature is difficult to image in vivo with existing modalities due to the
lack of resolution and sensitivity. Here, we demonstrate the feasibility of transthoracic super-resolution ultrasound
localisation microscopy (ULM) of myocardial microvasculature and hemodynamics in a large animal model and in patients, using a cardiac phased array probe with a customised data acquisition and processing pipeline. A multi-level motion correction strategy was proposed. A tracking framework incorporating multiple features and automatic parameter initialisations was developed to reconstruct microcirculation. In two patients with impaired myocardial function, we have generated ULM images of myocardial vascular structure and flow with a resolution that is at the wave-diffraction limit (half a wavelength), using data acquired within a breath hold. Myocardial ULM has potential to improve the understanding of myocardial microcirculation and the management of patients with cardiac microvascular diseases.