Diagnosing cancer therapy-related cardiovascular toxicities may be a challenge. The interplay between cancer and cardiovascular diseases, beyond shared cardiovascular and cancer risk factors, and the increasingly convoluted cancer therapy schemes have complicated cardio-oncology. Biomarkers used in cardio-oncology include serum, imaging and rhythm modalities to ensure proper diagnosis and prognostic stratification of cardiovascular toxicities. For now, troponin and natriuretic peptides, multimodal cardiovascular imaging (led by transthoracic echocardiography combined with cardiac magnetic resonance or computed tomography angiography) and electrocardiography (12-lead or Holter monitor) are cornerstones in cardio-oncology. However, the imputability of cancer therapies is sometimes difficult to assess, and more refined biomarkers are currently being studied to increase diagnostic accuracy. Advances reside partly in pathophysiology-based serum biomarkers, improved cardiovascular imaging through new technical developments and remote monitoring for rhythm disorders. A multiparametric omics approach, enhanced by deep-learning techniques, should open a new era for biomarkers in cardio-oncology in the years to come.