During early apoptosis, adult cardiomyocytes show unusual beating, suggesting a possible participation of abnormal Ca²⁺ transients in initiating apoptotic processes in this cell type. Simultaneous with the beating, these cells show dynamic structural alteration resulting from cytoskeletal disintegration that is quite rapid. Given how specialized and extensive the cytoskeleton of cardiomyocytes is, we hypothesized that its degradation in so short a time would require a particularly efficient mechanism. To better understand that mechanism, we used serial video microscopy to observe -adrenergic stimulation-induced apoptosis in isolated adult rat cardiomyocytes while simultaneously recording the intracellular Ca²⁺ concentration ([Ca²⁺]i) and cell length. Trains of Ca²⁺ transients and corresponding rhythmic contractions and relaxations (beating) were observed in the apoptotic cells. The frequencies of both the Ca²⁺ transients and the beating gradually increased with time and were accompanied by cellular shrinkage. In addition, as the cells shrank, the amplitudes of Ca²⁺ transients declined and the diastolic [Ca²⁺]i increased until the transients were lost. The beating and progression of apoptosis were significantly inhibited by antagonists against the L-type Ca²⁺ channel (nifedipine), ryanodine receptor (ryanodine), inositol 1,4,5-triphosphate receptor (heparin), sarcoplasmic Ca²⁺-ATPase (thapsigargin) and Na⁺/ Ca²⁺ exchanger (KB-R7943). Electron microscopic examination of beating cardiomyocytes revealed progressive breakdown of the Z discs. Immunohistochemical analysis and Western blotting confirmed that disappearance of Z disc constituent proteins (-actinin, desmin and tropomyosin) preceded degradation of the other cytoskeletal proteins. It thus appears that in adult cardiomyocyte apoptosis Ca²⁺ transients mediate apoptotic beating and the efficient sarcomere destruction initiated by Z disc breakdown.