Atrial fibrillation (AF) is one of the most frequent complications following coronary artery bypass grafting (CABG), occurring in up to 40% of patients. This thesis investigates the utility of non-invasive markers of left ventricular filling pressure in predicting AF in this setting, and assesses a novel marker of inflammation in the same role. Given the haemodynamic changes occurring peri-operatively it was hypothesised that acute changes in left ventricular filling pressure (LVFP), and resulting atrial stretch, might predispose to post-operative AF. Levels of the natriuretic peptides, BNP and NT-proBNP, were measured pre-operatively in 275 patients undergoing non-emergency CABG, and detailed echocardiographic examination performed. The natriuretic peptides were higher in patients who developed AF, and both were independently predictive of post-operative AF in multivariable analysis. However, their clinical utility appears modest in this role. The only significant echocardiographic predictors of AF were the transmitral E to A-wave ratio and the early mitral annulus velocity. None of the echocardiographic parameters remained independently predictive in multivariable analysis. The strongest echocardiographic correlate of both BNP and NT-proBNP was the left atrial volume index (LAVi), a marker of chronic LV filling pressure. Patients undergoing CABG are subject to a significant peri-operative inflammatory response. This was investigated in the same cohort by means of the neutrophil/lymphocyte (N/L) ratio. Patients who developed AF had greater pre- and post-operative N/L ratios, with no preoperative differences observed in other white blood cell parameters or C-reactive protein. In multivariate models, a greater post-operative N/L ratio was independently associated with the incidence of AF. In patients undergoing CABG, AF remains difficult to predict from pre-operative variables, although age appears to be a consistent factor. Difficulties in the prediction of AF in this setting are likely to reflect the heterogeneity of influences on the development of the arrhythmia in this setting.