Four-dimensional ultrasound and cardiac ultrasound are very different, as follows: 1. Four-dimensional ultrasound is an imaging technology in terms of dimensionality, which currently includes one-dimensional imaging, two-dimensional imaging, three-dimensional imaging, and four-dimensional imaging. The imaging mode of one-dimensional imaging is in the form of waves; the imaging mode of two-dimensional imaging is in the form of tangential surfaces; three-dimensional imaging is in the form of spatial stereo; four-dimensional imaging is real-time dynamic three-dimensional imaging, which means that the dimensional parameters of time are added on the basis of three-dimensional static imaging, that is, dynamic real-time three-dimensional. As long as the machine equipment allows, any part of the ultrasound examination can be imaged in four dimensions; 2. Cardiac ultrasound refers to the ultrasound of a certain part, such as cardiac ultrasound, liver ultrasound, kidney ultrasound, thyroid ultrasound, breast ultrasound and so on, in terms of parts. The imaging mode of cardiac ultrasound can be M-type, 2D, 3D, 4D, etc. The examination channel of cardiac ultrasound can be transthoracic ultrasound to examine the heart or transesophageal ultrasound to examine the heart, and there is a crossover between the two, which means that 4-dimensional ultrasound imaging can be applied to ultrasound examination of the heart and cardiac ultrasound can also perform 4-dimensional imaging.