The present invention relates to a new diagnostic X-ray composition which exhibits a superior cardiac safety profile. The composition comprises a non-ionic iodinated dimer in a pharmaceutically acceptable carrier. More particularly, the invention provides a diagnostic composition comprising a Compound I, a pharmaceutically acceptable carrier, and dissolved therein a sodium compound and a calcium compound providing a sodium ion concentration of 40-50 mM and a calcium ion concentration of 0.1-0.7 mM. The invention also relates to methods of imaging using such diagnostic compositions.
