This study proposes an ultrasound left ventricular segmentation method. First, the region of the heart with a different echo intensity is divided into independent parts by the three-phase Level Set method. Second, the ventricular wall region is extracted by the binary processing method, and the noise and myocardial wall area are removed and connected, respectively. Third, the left ventricle contour is fitted by the curve fitting method and segmented into a smooth closed segmentation curve. The segmentation results of the proposed algorithm are compared with the doctor's manual segmentation results. The left ventricle is qualitatively segmented. The results are evaluated using three image segmentation evaluation methods, namely, the relative difference degree (RDD), relative overlap degree (ROD), and Dice parameters. The RDD value is 0.051, while the ROD and Dice parameter values are both close to 0.900. The left ventricular segmentation results are quantitatively analyzed. The analysis shows that the algorithm has a good segmentation effect on the heart ventricular wall area, and it is not sensitive to intracardiac noise. A variety of curve fitting methods have a good effect on the left ventricular contour.