The spatial QRS-T angle (QRS-Ta), is a risk marker for ventricular arrhythmia and sudden cardiac death. QRS-Ta peak is the angle between QRS and T-wave loop maximal amplitudes using the vectorcardiogram, and captures information on ventricular depolarisation and repolarisation. It is hypothesised a wider QRS-Ta is due to local variation in action potential duration (APD), conduction velocity and cardiomyocyte morphology. However, no intra-cardiac evaluation of parameters influencing the QRS-Ta has previously been performed. Comparisons were made between QRS-Ta peak and intra-cardiac unipolar electrocardiograms (UEG) parameters simultaneously recorded in the right ventricle, left ventricle (LV) endocardium and LV epicardium (coronary sinus) in 10 patients with structurally normal hearts. Standard S1S2 restitution protocols were conducted by LV pacing at intervals decrementing from 1000ms to the effective refractory period (ERP). Repolarisation time (RT), activation time (AT) and activation-recovery interval (ARI) a surrogate for APD, were calculated. Dispersion of RT (DRT) was calculated as latest minus earliest RT. Two patients were excluded due to significant ectopy. Decreasing cycle length (CL) correlated with an increase in QRS-Ta (-0.56, -0.74 - -0.42, median, interquartile-range, P<0.02). Two phases were identified 1) a stable QRS-Ta between CLs 1000 to 400ms (144.06°, 142.63 – 146.87), 2) a rapid increase in QRS-Ta with further decrements followed by a small decrease just prior achieving ERP (157.72°, 149.57 – 161.56). Plotted against pacing interval, the QRS-Ta distribution mirrored the repolarisation restitution curve. The QRS-Ta was negatively correlated with mean RT (-0.59, -0.81 - -0.34, P=0.023) and mean ARI (-0.72, -0.73 - -0.42, P<0.02). There was a positive correlation with DRT (0.47, -0.05 – 0.67) however this did not reach significance. This study highlights QRS-Ta trends according to pacing interval and an inverse association with changes in APD and RT, which may contribute to increased arrhythmic risk in individuals with a wider QRS-Ta.