The calcium (Ca )-paradox injury of the heart, induced by restoration of extracellular Ca after its short-term depletion, is known to provoke cardiomyocyte contracture. However, undetermined is how the Ca -paradox provokes such a distinctive presentation of myocytes in the heart. To address this, we imaged sequential intracellular Ca dynamics and concomitant structures of the subepicardial ventricular myocytes in fluo3-loaded, Langendorff-perfused rat hearts produced by the Ca paradox. Under rapid-scanning confocal microscopy, repletion of Ca following its depletion produced high-frequency Ca waves in individual myocytes with asynchronous localized contractions, resulting in contracture within 10 min. Such alterations of myocytes were attenuated by 5-mM NiCl , but not by verapamil, SEA0400, or combination of ryanodine and thapsigargin, indicating a contribution of non-specific transmembrane Ca influx in the injury. However, saponin-induced membrane permeabilization of Ca showed no apparent contracture despite the emergence of high-frequency Ca waves, indicating an essential role of myocyte-myocyte and myocyte-extracellular matrix (ECM) mechanical connections in the Ca paradox. In immunohistochemistry Ca depletion produced separation of the intercalated disc that expresses cadherin and dissipation of β-dystroglycan located along the sarcolemma. Taken together, along with the trans-sarcolemmal Ca influx, disruption of cell-cell and cell-ECM connections is essential for contracture in the Ca -paradox injury. 2+ 2+ 2+ 2+ 2+ 2+ 2+ 2+ 2+ 2+ 2+ 2+ 2+ 2+ 2