ATP-sensitive K⁺ (K_ATP) channels are essential for maintaining the cellular homeostasis against metabolic stress. Myocardial remodeling in various pathologies may alter this adaptive response to such stress. It was reported that transmural electrophysiological heterogeneity exists in ventricular myocardium. Therefore, we hypothesized that the K_ATP channel properties might be altered in hypertrophied myocytes from endocardium. To test this hypothesis, we determined the K_ATP channel currents using perforated patch-clamp technique, open cell-attached patches, and excised inside-out patches in both endocardial and epicardial myocytes isolated from hypertrophied (spontaneous hypertensive rats: SHR) vs normal (Wistar Kyoto rats: WKY) left ventricle. In endocardial cells, K_ATP currents (I_K,ATP), produced by 2 mM CN^- and no glucose at 0 mV, were significantly smaller (p<0.01) and time required to reach peak currents after onset of K_ATP channels opening (Time_{onset to peak}) were significantly longer (319 ± 46 vs 177 ± 37 seconds, p=0.01) in SHR group (n=9) than WKY group (n=13). However, in epicardial cells, there were no differences in I_K,ATP and Time_{onset to peak} between the groups (SHR, n=12; WKY, n=12). The concentration-open probability response curves obtained during the exposure of open cells and excised patches to exogenous ATP revealed the impaired K_ATP channel activation in endocardial myocytes from SHR. In conclusion, the K_ATP channel activation under metabolic stress was impaired in endocardial cells from rat hypertrophied left ventricle. The deficit of endocardial K_ATP channels to decreased intracellular ATP might contribute to the maladaptive response of hypertrophied hearts to ischemia.