Reduced Left Atrial Emptying Fraction and Chymase Activation in Pathophysiology of Primary Mitral Regurgitation

•Extensive LA fibrosis is related to an increase in LA size and decrease in total LA EF. This supports the contention that the LA is not merely a bystander of MR but rather is actively involved in the pathophysiology of MR.•Chymase is plentiful in the human heart, especially in the LA, and correlates with extracellular matrix accumulation in primary MR.•Because of the unreliability of the LV ejection fraction in primary MR, future studies may consider LA size and total LA EF for timing of surgical intervention of asymptomatic moderate to severe MR.