Magnetic resonance T(2)* has been validated as a noninvasive means of assessing myocardial iron overload. However, the effect on myocardial T(2)* of factors such as shimming, variations in capillary geometry, and susceptibility in relation to the effects of iron has not been fully clarified. Since T(2) is not affected by extrinsic magnetic field inhomogeneity and has different sensitivity to capillary geometry, investigation into the in vivo relationship between myocardial T(2)* and T(2) measurements can shed light on this important issue. This study was performed in 136 thalassemia patients. The myocardial T(2) and T(2)* thresholds for normality created identical no-iron-overload and iron-overloaded patient groups. In the no-iron group, there was no correlation between myocardial T(2) and T(2)*. In the iron-overloaded patients, there was a linear correlation (R(2) = 0.89) between myocardial T(2)* and T(2) measurements, which indicates that the iron deposition is the dominant factor in determining these two relaxation values in this scenario.