We found a correlation between left and right atrial fibrosis (r (s) = 0.79, p<0.01). Interestingly, the higher the interstitial collagen content, the higher was the spatial heterogeneity of fibrosis (r (s) = 0.90, p<0.001). However, PICP, PIIINP, and ICTP were not correlated to left or right atrial collagen content, or to the spatial heterogeneity of atrial fibrosis