Introduction: We intended to assess the ability of current generation 256-slice coronary computed tomographic angiography (CCTA) to measure LA volume (LAV) comparing patients with high heart rate (HiHR) of > 70bpm and heart rate variability such as atrial fibrillation (AFib). Methods: Using the prospective CONVERGE Registry of patients undergoing 256 detector CCTA (Revolution, GE Healthcare, Milwaukee WI), we enrolled 121 high HR patients (74 men; mean age 62.7+12.5yrs) and 102 patients with AFib (72 men; mean age 60.5+11.0yrs) after obtaining the informed consent. Quantitative data analyses of LAV was performed using automated methods on a workstation and software (AW4.6; GE Medical Systems, Waukesha, WI, USA) and end-systolic phases were chosen for measurements from CCTA. A student's t test, Wilcoxon rank-sum or chi-square tests assessed baseline parameters. Univariate and multivariate linear regression analysis was used to assess LAV and LAV index (LAVI) while adjusting potentially confounding variables. Results: Mean LAV in AFib subjects was significantly higher (148.6 ± 57.2mL), compared to HiHR subjects (102.1 ± 36.5mL), p<0.0001. Similarly, mean LAVI in AFib subjects was significantly higher (72.4 ± 28.1 ml/m2) than HiHR subjects' LAVI, (51.5 ± 19.0 ml/m2) p<0.0001. After adjusting age, BMI, gender, diabetes, hypertension, hyperlipidemia, and smoking and those with AFib had on average higher LAV measures by 41.2±6.7 mL and LAVI by 23.1±3.4 ml/m2, p<0.0001. Conclusion: Misalignments and motion artifacts of CCTA images affects the CT diagnostic performance especially in patients with elevated heart rates or profound arrhythmia. However, the new generation Revolution CCTA provides the detailed LA complex morphology and function in HiHR and AFib patients in addition to coronary anatomy without additional radiation, scanning or contrast requirements.