Objective: The aim of the here proposed study is to clarify whether cardiac function in survivors of BC should be monitored by GPs, by assessing whether an unselected population of long-term BC survivors is at increased risk of developing cardiac dysfunction, whether in this group at-risk subgroups exists, and what factors are associated with the highest risk. Study design: A new assessment of cardiac function among women included in the BLOC-I study. This produces a longitudinal matched cohort design consisting of two cohorts in primary care. Study population: Survivors of BC, diagnosed ≥11 years ago who received chemotherapy and/or radiotherapy, and a matched reference population with no history of cancer. All participants participated in the Breast cancer Long-term Outcome of Cardiac function (BLOC-I) study. Main study parameters/endpoints: Left ventricular systolic dysfunction. Systolic cardiac dysfunction is defined as a LVEF \<54/50/45%.