Will a heart mri detect breast cancer?

Unlikely: Breast MRI is a very sensitive test for breast cancer detection, using special software and thousands of images to be effective. An MRI of the heart, not unlike a ct scan, can serendipitously find an abnormality in the breast but, since it is not specifically "looking" for breast abnormalities, would be less reliable than a simple mammogram or ultrasound.

Not likely: The equipment used for cardiac scanning, with ct used more than MRI i believe, is usually focused just on the heart structures. So breast evaluation during a heart scan is not likely and the equipment may not be designed to evaluate the breast tissue either.

No : Mri of the breast required to look at breast tissue appropriately. See radiologyinfo.Org.