High-resolution three-dimensional (3D) imaging of cardiovascular dynamics in mouse embryos is greatly desired to study mammalian congenital cardiac defects. Here, we demonstrate direct four-dimensional (4D) imaging of the cardiovascular structure and function in live mouse embryos at a ∼43 Hz volume rate using an optical coherence tomography (OCT) system with a ∼1.5 MHz Fourier domain mode-locking swept laser source. Combining ultrafast OCT imaging with live mouse embryo culture protocols, 3D volumes of the embryo are directly and continuously acquired over time for a cardiodynamics analysis without the application of any synchronization algorithms. We present the time-resolved measurements of the heart wall motion based on the 4D structural data, report 4D speckle variance and Doppler imaging of the vascular system, and quantify spatially resolved blood flow velocity over time. These results indicate that the ultra-high-speed 4D imaging approach could be a useful tool for efficient cardiovascular phenotyping of mouse embryos.