Ion transport cycle and inactivation reactions of the cardiac (NCX1) Na/Ca exchanger. The transport cycle (states 1 to 4) moves one Ca outwardly and three Na ions inwardly. Inactivation occurs preferentially when three Na are bound to the inwardly facing transport sites and anionic phospholipids such as PIP₂ are depleted (states 4 to 5). A second inactivation process occurs preferentially when regulatory Ca binding sites are not occupied by Ca (states 4 to 7 and 5 to 6). The two inactivation processes are interactive and reinforce one another.