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Aim: As acute short-lived increase in afterload may be a contributory mechanism to sudden death, we studied an acute 30% systolic pressure increase (SBPI) in a closed chest, closed pericardium porcine model, closed pericardium being essential to the model clinical applicability. Methods: 7 pigs were studied. All had an acute 5 beat 30% SBPI induced by a non-occlusive mid- descending aortic balloon inflation and release. Each challenge was continuously monitored for changes in cardiac morphology and function by cardiac ultrasound (2D, Doppler and Doppler Myocardial Imaging) and changes were correlated with pressure data from 3 Millar catheters (LV/Ao ; LA ; RV/RA). Continuous 12 lead ECG and intracardiac electrograms were also recorded. Results: Balloon inflation caused an acute diastolic pressure increase in all cavities (except pulmonary artery) with early diastolic preceding late changes and a corresponding systolic increase in LV, LA and RA pressures. Acute LV dilatation resulted in pericardial flattening (which is a visualization of the effects of pericardial constraint), a septal shift towards the RV and a decrease in RV size with a 30% reduction in LVEF % (Fig1a). During inflation, pericardial excursion flattened > 40% in basal, mid and apical LV segments, mostly mid wall (from 3.4±1.4 mm to 1.6±0.7 mm, p