Objective: To investigate the efficacy of three-dimensional transesophageal echocardiography (3D-TEE) in evaluating the extent of stenosis in pannus on artificial mechanical valves. Methods: A total of 46 cases with pannus on the prosthetic heart valve diagnosed via transesophageal echocardiography (TEE), confirmed surgically in our hospital between October 2019 and March 2023, were recruited. This cohort included 12 cases of pannus on the prosthetic mitral valve and 22 cases of pannus on the prosthetic aortic valve. The 3D-TEE imaging characteristics of pannus were observed, and various parameters were measured, including pannus area, the ratio of the areas of the medial and lateral edges of the annulus, and the ratio of the pannus width to the valve external diameter (W/D). Additionally, the mean transvalvular pressure gradient was measured via transthoracic echocardiography (TTE). The study analyzed and compared the correlation between these parameters of the pannus and the mean transvalvular pressure gradient (mTPG). Results: ① The 3D-TEE results revealed that a pannus angle encompassing the prosthetic valve annulus, equal to or exceeding 180°, was associated with a higher likelihood of pronounced stenosis in the valve orifice. The angle size was significantly associated with the degree of stenosis (P < 0.05). ② In prosthetic aortic valves, it was found that the three key measurements - the ratio of the areas of the medial and lateral edges of the annulus being 0.33±0.08, W/D of the pannus at 0.41±0.09, and the area of the pannus being 1.79±0.68 cm2 - strongly correlated with the mTPG of 44.13±13.59 mmHg. The correlation coefficients for these combined parameters were R=-0.782, P<0.001, R=0.820, P<0.001, and R=0.741, P<0.001, respectively. In artificial mitral valves, it was observed that the concurrent presence of the following three measurements - the ratio of the areas of the medial and lateral edges of the annulus at 0.31±0.07, the W/D of the pannus at 0.35±0.09, and the area of the pannus at 1.88±0.71 cm2 - significantly correlated with the mTPG of 13.87±6.59 mmHg. The combined correlation coefficients for these parameters were R=-0.793, P<0.001, R=0.878, P<0.001, and R=0.806, P<0.001, respectively. ③The correlation between parameters related to the pannus in prosthetic mitral valves and the mTPG gradient was stronger compared to that in prosthetic aortic valves. Conclusion: 3D-TEE is valuable for assessing the extent of stenosis in pannus on prosthetic valves. Particularly, the pannus W/D index can accurately assess the degree of valve obstruction. The study suggests that 3D-TEE is more valuable for evaluating the degree of pannus obstruction in prosthetic mitral valves than that of prosthetic aortic valves.