Patients will be recruited from the clinics run by University Hospitals Birmingham NHS Foundation Trust (UHB) with stages 2, 3, 4 and 5 CKD defined using eGFR calculated with the 4-variable 'Modification of Diet in Renal Disease' (MDRD) equation, with a minimum of two consecutive tests at least 90 days apart. Forty patients will be recruited per group of CKD. All study subjects will undergo a cardiac MRI scan, a cardiopulmonary exercise tests with stress echocardiogram, a 24-hour ECG holter monitor, and blood tests.