1. A method to determine a magnetic resonance (MR) relaxation time in a heart muscle in a magnetic resonance examination, comprising the steps of: providing a computerized processor with magnetic resonance data representing at least a portion of the heart muscle of a left heart chamber of an examination subject and, in said processor, implementing an automatic image segmentation of said magnetic resonance data to determine an annular slice image region of the heart muscle of the left heart chamber; in said processor, automatically dividing said slice image region of the heart muscle of the left heart chamber into a plurality of sub-regions, each sub-region comprising a plurality of pixels of said annular slice image region of the heart muscle of the left heart chamber; in said processor, automatically determining, for each of said sub-regions, an MR relaxation time of muscle tissue in the respective sub-region, thereby obtaining a plurality of MR relaxation times; and in said processor, automatically determining an MR relaxation time in the heart muscle by statistical analysis of said plurality of MR relaxation times of the sub-regions.