Calcium signaling in the vascular endothelium regulates vascular growth, immune responses, and tone. Endothelial cells (ECs) are mechanosensitive, and flow-driven shear stress is widely assumed to be the main trigger for EC Ca responses in vivo. Vascular ECs experience a range of distinct mechanical forces in vivo. These include shear stress from blood flow, radial stretch from blood pressure, circumferential stretch from smooth-muscle-mediated vasodilation, and, in some parts of the animal, axial stretch from skeletal-muscle-mediated body motion In principle, these different modes of stimulation could activate distinct signaling pathways and cellular responses. Mechanical perturbation experiments on cultured cells or explants typically impose stresses that differ in magnitude and direction from the forces encountered in vivo, and thus they cannot readily be used to assign biochemical responses to specific sources of mechanical stress in vivo. Here, we show that, in larval zebrafish, the dominant trigger for vascular endothelial Ca events comes from body motion, not heartbeat-driven blood flow. Through a series of pharmacological and mechanical perturbations, we showed that body motion is necessary and sufficient to induce endothelial Ca events, while neither neural activity nor blood circulation is necessary or sufficient. CRISPR-Cas9 knockout and temporally restricted photomorpholino knockdown identified Piezo1 as necessary for the rapid, mechanically evoked EC Ca events. Our results demonstrate that swimming-induced tissue motion is an important driver of endothelial Ca dynamics in larval zebrafish. Copyright © 2025 Elsevier Inc. All rights reserved.