Relaxation of DCM samples with truncating mutations in the TTN gene was not different from control, while relaxation was faster in all other studied myofibrils which had mutations in the genes of contractile proteins: myosin (MYH7 E1426K) and troponins (TNNI3 K36Q and TNNC1 G159D). Here, TNNI3 is linked to familial dilated cardiomyopathy.