Background: The extracardiac accumulation masking (MUS) method reduces artifacts from extracardiac accumulation by masking post-reconstruction and filtering. However, the impact of filter parameters on defect scores and cardiac function remains unclear. Thus, this study aimed to evaluate the effect of noise reduction filters in MUS on the defect score and left ventricular volume. Methods: To simulate the defect area, an RH-2 cardiac phantom (Kyoto Kagaku, Japan) was used with 99mTc solutions for the heart and liver. The heart-liver distance was varied (0, 1, and 2 ㎝). SPECT/CT and image reconstruction was performed using filtered back projection (FBP) with a Butterworth filter. The cut-off frequencies (0.3 to 0.7 cycles/㎝) were applied for both conventional and MUS methods. And a summed score (SS) and the left ventricular volume was employed as evaluation metrics. Results: SS values were more stable with the MUS methods than the conventional methods, especially at distances of 1 and 2 ㎝. Left ventricular volume increased with higher cut-off frequencies with no significant differences between MUS and conventional methods. Conclusion: The MUS method can reduce the impact of different cut-off frequencies on the defect score.