We assessed the relationship between J waves and the ventricular morphology and function using cardiac magnetic resonance imaging (MRI). The 12-lead electrocardiograms (ECGs) of 105 consecutive patients who underwent cardiac MRI were reviewed, and those with signs of arrhythmogenic right ventricular cardiomyopathy, complete left bundle branch block, complete right bundle branch block, or chronic atrial fibrillation, where the J wave is difficult to distinguish, were excluded. The ECGs of the remaining 68 patients were analyzed for the presence of J waves. Ventricular morphologic abnormalities were identified on MRI, based on the largest short-axis diameter in the right and left ventricles (d-RVmax/d-LVmax), the area (a-RVmax/a-LVmax), and the ratio RV/LVmax. The percentage contraction of the RV (PC-RV) was used as a measure of ventricular function. Thirty-two patients (47.0 %) had J waves defined as QRS-ST junction elevation >0.1 mV from baseline in the inferior/lateral leads (J group; 56 ± 15 years; 19 males). Thirty-six patients (53.0 %) did not present J waves (NJ group; 58 ± 15 years; 27 males). The d-RVmax and a-RVmax in the J group were larger than those in the NJ group (41 ± 5.2 vs 36 ± 6.6 mm, P = 0.002 and 14 ± 2.9 vs 12 ± 3.4 cm(2), P = 0.022, respectively). The RV/LVmax ratio in the J group was larger than that in the NJ group (0.83 ± 0.15 vs 0.68 ± 0.15, P < 0.001). The PC-RV in the J group was smaller than that in the NJ group (0.28 ± 0.14 vs 0.36 ± 0.15, P = 0.013). J-wave amplitude was correlated positively with d-RVmax (P = 0.010) and negatively with PC-RV (P = 0.005). These results suggested that J waves are associated with right ventricular morphologic and functional abnormalities.