ALT eXplainMR is a Mixed Reality tutoring system designed for basic cardiac surface ultrasound training. Trainees wear a head-mounted display (HMD) and hold a controller, mimicking a real ultrasound probe, while treating a desk surface as the patient’s body for low-cost and anywhere training. eXplainMR engages trainees with troubleshooting questions and provides automated feedback through four key mechanisms: 1) subgoals that break down tasks into single-movement steps, 2) textual explanations comparing the current incorrect view with the target view, 3) real-time segmentation and annotation of ultrasound images for direct visualization, and 4) the 3D visual cues provide further explanations on the intersection between the slicing plane and anatomies.