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The aim of this work is to study the influence of activation of the ATP-sensitive potassium (K/sub ATP/) current on vulnerability to reentry during cardiac hypoxia. A detailed mathematical model of this current was introduced into the Luo-Rudy model of the cardiac action potential (AP), and the electrical activity in a 1D ring of cardiac tissue was simulated. To reproduce the natural dispersion of the sensitivity of the K/sub ATP/ current to [ATP]/sub p/ the half-maximum inhibition constant of the channel was randomized following a Gaussian distribution. Hypoxia was simulated by appropriately reducing [ATP]/sub l/ and increasing [ADP]/sub r/. The simulated hypoxic APs show a significant shortening compared to control APs, and spatial inhomogeneity of action potential duration (APD) is enhanced by inhomogeneous K/sub ATP/ current activation. Moreover, the authors' results show that the hypoxic APD dispersion caused by opening of K/sub ATP/ channels could be enough to elicit reentrant activity.