Mechanoelectric transduction can initiate cardiac arrhythmias. To examine the origins of this effect at the cellular level, we made whole cell voltage-clamp recordings from acutely isolated rat ventricular myocytes under controlled strain. Longitudinal stretch elicited noninactivating inward cationic currents that increased the action potential duration. These stretch-activated currents could be blocked by 100 µM Gd³⁺ but not by octanol. The current-voltage relationship was nearly linear, with a reversal potential of approximately 6 mV in normal Tyrode solution. Current density varied with sarcomere length (SL) according to I (pA/pF) = 8.3  5.0SL (µm). Repeated attempts to record single channel currents from stretch-activated ion channels failed, in accord with the absence of such data from the literature. The inability to record single channel currents may be a result of channels being located on internal membranes such as the T tubules or, possibly, inactivation of the channels by the mechanics of patch formation.