Objective To explore the application of magnetic resonance imaging (MRI) and 64-slice spiral CT in evaluation of left cardiac function in old myocardial infarction. Methods 150 cases of patients with old myocardial infarction in our hospital were selected for the study and were given MRI and 64-slice spiral CT examinations. The left cardiac function [ left ventricular end diastolic volume (EDV), end systolic volume (ESV), stroke volume (SV), ejection fraction (EF) and diastolic myocardial mass (MM)] were detected, and the MRI results were taken as the standard, the validity and consistency of detection results of 64 slice spiral CT were evaluated. Results There was no significant difference in EDV, ESV, SV, EF, MM and MRI results between 64-slice spiral CT and MRI (P>0.05), and the correlation r values were 1.843, 1.217, 1.405, 1.985 and 1.326 respectively (P<0.05). The EF<50% of MRI results was taken as the standard, and the sensitivity, specificity, accuracy, positive prediction value and negative predictive value by 64-slice spiral CT detection were 100% (71/71), 96.20% (76/79), 98.00% (147/150), 95.95% (71/74) and 100% (76/76). The consistency between 64-slice spiral CT findings and MRI findings was not significantly different (κ=1.428, P>0.05). Conclusion 64-slice spiral CT can have high sensitivity and accuracy in the evaluation of left heart function in patients with old myocardial infarction, and it can have reliable results and good consistency with MRI.