Purpose To implement and evaluate a new dictionary-based technique for native myocardial T-1 and T-2 mapping using Cartesian sampling. Methods The proposed technique (Multimapping) consisted of single-shot Cartesian image acquisitions in 10 consecutive cardiac cycles, with inversion pulses in cycle 1 and 5, and T-2 preparation (TE: 30 ms, 50 ms, and 70 ms) in cycles 8-10. Multimapping was simulated for different T-1 and T-2, where entries corresponding to the k-space centers were matched to acquired data. Experiments were performed in a phantom, 16 healthy subjects, and 3 patients with cardiovascular disease. Results Multimapping phantom measurements showed good agreement with reference values for both T-1 and T-2, with no discernable heart-rate dependency for T-1 and T-2 within the range of myocardium. In vivo mean T-1 in healthy subjects was significantly higher using Multimapping (T-1 = 1114 +/- 14 ms) compared to the reference (T-1 = 991 +/- 26 ms) (p < 0.01). Mean Multimapping T-2 (47.1 +/- 1.3 ms) and T-2 spatial variability (5.8 +/- 1.0 ms) was significantly lower compared to the reference (T-2 = 54.7 +/- 2.2 ms, p < 0.001; spatial variability = 8.4 +/- 2.0 ms, p < 0.01). Increased T-1 and T-2 was detected in all patients using Multimapping. Conclusions Multimapping allows for simultaneous native myocardial T-1 and T-2 mapping with a conventional Cartesian trajectory, demonstrating promising in vivo image quality and parameter quantification results.