Arrhythmia in heart cells is a potentially life-threatening condition. The contraction of cardiac cells is chiefly regulated by calcium, whose release and subsequent reuptake is tightly controlled by various cellular components. When these components do not coordinate well, rhythmic disorders may result. A new paper, to appear in Biophysical Journal, studies the role of calcium stores in cellular organelles called lysosomes, and how the interaction between lysosome calcium release, ryanodine receptors and uptake by the sarcoplasmatic reticulum gives rise to abnormal calcium transients. This work is a collaboration with cardiophysiologists at Oxford University; VU mathematics students Sophia de Jong and Erik Bosch contributed to the modelling and simulations during their bachelor thesis, under the guidance of Bob Planqué. A rare treat that BSc thesis work gets published!