Inclusion Criteria:  Age ≥ 18 years Mutations in the TTN gene leading to truncating variants in cardiac expressed exons of titin. A clinical diagnosis of dilated cardiomyopathy or fulfulling criteria for the diagnosis of heart failure or hypokinetic non-dilated cardiomyopathy.  Exclusion Criteria:  New York Heart Association functional class IV. Patients with a left ventricular assist device or who have had a heart transplant. Change in heart failure medications within the last month. CRT implantation within the last 6 months. Inability to perform exercise due to orthopedic or other non-cardiovascular limitations. Clinical history of exercise-induced syncope likely caused by ventricular tachyarrhythmias. Current participation in moderate or high intensity exercise exceeding 2.5 hours/per week. Inability to give informed consent. Pregnant women. Severe vascular disease (IE claudicatio intermittens). Severe valvular disease (moderate aortic stenosis/regurgitation or severe mitral regurgitation/stenosis). Life expectancy less than 12 months. Expected reduced compliance.