We show that credit score heterogeneity dampens monetary policy transmission through fixed-rate mortgages (FRMs). Using Fannie Mae Single-Family Loan-Level historical data, we show that a one-percentage-point reduction in the mortgage rate increases the refinancing probability for borrowers with excellent credit scores twice as much as it does for borrowers with good credit scores. We then develop a refinancing model and find that credit score heterogeneity dampens consumption response to monetary policy through the FRM channel by one-third and results in a 50% higher wealth increase for excellent borrowers compared to good ones in the long run. Borrowers with lower credit scores have higher marginal propensities to consume and benefit from refinancing more than borrowers with higher credit scores, but refinance less often, resulting in smaller consumption and wealth responses.