Inclusion Criteria:  Age >18 years old. Suitable to have either a single chamber pacemaker or single chamber cardioverter-defibrillator.  Exclusion Criteria:  BMI >30. Pregnancy. Implantation of dual-chamber and CRT devices. Claustrophobia. Tender chest wall or history of trauma to the chest wall. Higher signal interference using ultrasound due to the presence of other medical devices or tools used in previous surgical procedures such as sternal wires, mechanical valves, breast implants. History of radiation to the chest wall for oncology treatments. Active malignancy