The presented study explores correlations and differences of myocardial blood flow measured with MRI and PET. We employed a post-processing method to estimate the arterial input function using gamma variate model. Rest/stress quantitative PET/MRI cardiac perfusion study were simultaneously performed on sixteen patients with myocardial ischemia. The results demonstrated the feasibility of the new AIF estimation method for the quantification of MBF by MRI without using special sequences or dual bolus injections of contrast media. Statistical analysis between PET and MRI data demonstrated good correlation with a linear trend and error ranges comparable to those previously reported in the literature.