[en] This thesis has described the use of Magnetic Resonance Imaging (MRI) in the investigation of left ventricular dimensions and systolic function. This has been performed in conditions of left ventricular dysfunction, in congestive cardiac failure and following anterior myocardial infarction. The reproducibility of measurements of left ventricular dimensions using MRI has been presented. Such measurements were shown to be reproducible between different MRI studies of normal volunteers and patients with congestive heart failure. Furthermore, measurements from different MRI studies obtained from two commercially different systems were reproducible for the same subject groups. Ventricular dimensions and systolic function was evaluated in adult normal volunteers of different ages. Although left ventricular volumes and mass remained unchanged, detailed studies of the systolic images revealed significant differences between the two age groups. Differences in left ventricular cavity volumes and mass between patients with congestive heart failure and age-matched normal volunteers were also investigated. Left ventricular volumes and myocardial mass were assessed in a group of patients following anterior myocardial infarction. End-systolic volume was significantly increased compared to age-matched volunteers, but no changes in end-diastolic volume or myocardial mass was observed. Serial re-evaluation of these patients revealed no other changes over the subsequent six months. All these patients were treated with optimal medical therapy (thrombolysis, aspirin, beta-blockade and angiotensin converting enzyme inhibition). Thus, the use of this therapy may attenuate the process of left ventricular remodelling. Regional wall thickness was measured in the post-infarct patients. Wall thickening was significantly reduced both in the infarcted regions and in myocardium remote to the infarction. In contrast to previous echocardiographic studies, no 'hypercontractility' was observed at any stage over the study period. Furthermore, neither infarcted or remote myocardium demonstrated full recovery back to normal. (author)