Background: Natriuretic peptide (NP) levels have been proposed for characterization and risk stratification of heart failure (HF) among patients with cardiovascular disease (CVD). However, their role in patients with diabetes mellitus type 2 (T2DM) has not been well studied and understood. The aim of this study was to assess phenotypical, functional characteristics and imaging parameters in relation to N-terminal pro b-type natriuretic peptide (NT-proBNP) values in T2DM patients without known CVD that may predispose to overt HF. Methods: This was a cross-sectional study of 100 consecutive T2DM patients (mean overall age of 67 ± 9 years, 40% women and 60% men) who were enrolled from the outpatient diabetic clinic. Patients underwent a cardiopulmonary exercise test (CPET), and echocardiographic and cardiac magnetic resonance imaging (CMR); serum NT-proBNP was also measured. Results: The mean (standard deviation) NT-proBNP was 149 (±186) pg/mL. Patients in the highest tertile of NT-proBNP values (>107 pg/mL) had lower values of predicted maximum oxygen consumption compared to the lowest quartile (<55 pg/mL) (84% vs. 92%, p = 0.018) in the CPET and higher ratio of early diastolic mitral inflow velocity to early diastolic mitral annulus velocity (E/e′) (9.0 vs. 7.2, p = 0.05) in echocardiography. Finally, there was a negative correlation between right ventricle end diastolic volume in CMR and predicted maximum oxygen consumption (b = −0.225 ± 0.11, p = 0.046). Conclusions: NT-proBNP levels seemed to be a useful marker in people with T2DM, as elevated levels reflected ongoing appearance of HF with preserved ejection fraction and were related to CPET and echocardiographic indices of impaired left ventricular diastolic and right ventricular systolic function.