Abstract: The present invention relates to manganese-enhanced MRI, more specifically to a method for determining a cardiomyocyte cellular manganese uptake rate of a subject, contrast agent comprising a manganese contrast agent, or a pharmaceutically acceptable salt thereof, for use in a method for in vivo diagnosis of heart disease in a subject, a computer-implemented method of determining a cardiomyocyte cellular manganese uptake rate in a subject, a data processing apparatus comprising means for carrying out said computer-implemented method, a computer program comprising instructions which, when the program is executed by a computer, cause the computer to carry out said computer-implemented method, and a computer-readable medium having stored thereon said computer program.