Inclusion Criteria:  Age > 21 Electrophysiological diagnostic (mapping) and/or therapeutic (ablation) of epicardial sites via percutaneous subxiphoid approach to the to the normal, non-distended ericardial space is indicated.  Pre-treatment coagulation values within the following limits:  international normalized ratio 0.8 - 1.2 partial thromboplastin time 25 - 35''  Pre-treatment hematology and biochemistry values within the following limits:  hemoglobin ≥ 10 g/dL (g/100 mL) platelets ≥ 150 x 10^9/L (x 10^3/mm^3) white blood cells ≥ 3.0 x 10^9/L (x 10^3/mm^3) absolute neutrophil count (ANC) ≥ 1.5 x 10^9/L (1.5 x 10^3/mm^3) serum creatinine < 1.5 mg/dL aspartate aminotransferase < 1.5 x ULN (upper limit of norm) alanine aminotransferase < 1.5 x ULN alkaline phosphatase < 1.5 x ULN Signed informed consent.  Exclusion Criteria:  History of cardiac or pericardial surgery or prior pericardial ablation. History of chronic pericarditis. Known pericardial fibrosis and/or adhesions. Any anomaly in the chest anatomy. Myocardial infarction, past or present. Bleeding disorders. Hepatic enlargement. BMI > 40 Participation in another interventional trial. Pregnancy.