The primary objective of this study is to evaluate the agreement between hemodynamic measurements obtained using the Ultrasound Cardiac Output Monitor (USCOM®; USCOM Ltd., Sydney, Australia), and reference standards as determined by 2 Dimensional echocardiography (2D-echo) measurements in a group of hemodynamically stable and unstable pediatric patients.

2D-echo is the standard-of-care tool for non-invasive hemodynamic assessments in children. The use of 2D-echo requires highly trained personnel, and assessments may take anywhere between 30-45 minutes. The feasibility of real time hemodynamic assessments is therefore limited with 2D-echo. USCOM has been introduced as a non-invasive bedside hemodynamic monitoring tool that utilizes continuous-wave Doppler ultrasound. As USCOM is easily portable, and measurements take only several minutes and can be conducted by trained physicians or nurses, it has become an attractive method of real time hemodynamic monitoring of unstable patients. While USCOM validation studies have been conducted in adult, neonatal and pediatric populations, the following concerns have been raised: a) Pediatric data on the agreement between USCOM and other standard methods of CO measurement (i.e. 2D-echo, pulmonary artery catheterization) are conflicting with some studies reporting acceptable agreement, while others report poor agreement ; b) USCOM validation and agreement studies were previously conducted in primarily hemodynamically stable populations. Its performance in hemodynamically unstable and mechanically ventilated patients has not been studied to date in the pediatric population.USCOM is currently being promoted as a real-time tool for assessing hemodynamic status, and directing the care of unstable children without adequate evidence. Therefore, this study is essential to inform the validity of USCOM and whether it can or should be used when 2D-echo for real time hemodynamic monitoring in children is not feasible or available.

Inclusion Criteria:

• Age under 18 years
• Patient fulfills clinical criteria for either study cohort
• Most Responsible Physician has ordered an ECHO study on the patient
• Written informed consent by parents/legal guardian/substitute decision maker, and assent where appropriate
• Patients with normal cardiac structure, no pre-existing primary cardiovascular disease or hemodynamically insignificant shunt lesions (i.e. hemodynamically insignificant Atrial Septal Defect/Patent Foramen Oval and Ventricular Septal Defect

Exclusion Criteria:

• Age ≥ 18 years
• Premature infants (born <37 weeks gestation) admitted to the Neonatal Intensive Care Unit
• Known co-existing primary cardiac anomalies (i.e. aortic or pulmonary valve stenosis or regurgitation, Aortic Valve regurgitation, shunt lesions save for those mentioned above, and pericardial effusion)
• Prior enrollment in study

1. The hemodynamically stable group: will be screened from pediatric in-patients on McMaster Children's Hospital general pediatric wards and those scheduled for elective 2D-echo through cardiology and sedation clinic.
2. The hemodynamically unstable patients and 3. those requiring mechanical ventilation will be screened from McMaster Children's Hospital Pediatric Critical Care Unit.