Ibrutinib is an irreversible inhibitor of Bruton tyrosine kinase (BTK) that is indicated for multiple hematological malignancies, including previously untreated chronic lymphocytic leukemia (CLL). This drug is known to have cardiotoxic properties, probably due to off-target inhibition of another kinase. While in randomized trials ibrutinib has been demonstrated to increase survival, some studies have demonstrated fatal toxic effects associated with the drug. This was most obvious in a 3-arm study of CLL in which the 2 ibrutinib arms were associated with a 7% rate of death during treatment or within 30 days after treatment cessation, compared with a 1% rate of death in the control arm.1