Iron uptake in mitochondria and fractionated mitochondria compartments was studied to understand iron transport in heart mitochondria. The inner membrane is most active in iron uptake. Mitochondrial uptake was dependent on iron concentration and the amount of mitochondria. Iron transport was inversely proportional to pH in the range of 6.0 to 8.0. Iron transport reached a maximum after 30 min of incubation at $37^{circ}C$. Iron uptake was inhibited by 1 mM ATP and stimulated by 1 mM ADP. The oxidative phosphorylation inhibitor oligomycin inhibited iron uptake, but rotenone and antimycin A did not. The divalent ions $Mg^{2+}$, $Cu^{2+}$, $Mn^{2+}$, and $Zn^{2+}$ suppressed iron uptake at $10;{mu}M$ and stimulated it at 1 mM. The divalent ion $Ca^{2+}$ stimulated iron uptake at $10;{mu}M$ and suppressed it at 1 mM, competing with iron. The uptake of calcium was stimulated by 10 to $1000;{mu}M$ ATP, while iron uptake was stimulated reciprocally by 10 to $1000;{mu}M$ ADP, suggesting that these ions have movements similar to those of ATP and ADP.