This is a 2- component, single center study, witch aims to evaluate the efficacy of multisite intracardiac echocardiography (mICE) imaging of left atrial appendage (LAA) and in detecting thrombus located in LAA as compared to transesophageal echocardiography (TEE). The study group will consist of patients eligible for atrial fibrillation (AF) ablation procedure (Component I) or cardioversion (Component II).

First component will enroll 100 patients; these patients will undergo clinically indicated TEE & cardiac catheterization procedures with ICE(AF ablation). Second component will enroll 15-20 patients with AF or atrial flutter in whom a thrombus in LAA was detected by TEE prior to electrical cardioversion. The ICE probe will be located in multiple positions in the right atrium (RA), coronary sinus (CS), pulmonary artery (PA), right ventricular outflow tract (RVOT) and esophagus. This will enable the investigators to compare sensitivity and specificity of mICE and TEE.

This study will examine two hypotheses in AF patients undergoing invasive cardiac procedures:

Hypothesis 1: That ICE has comparable efficacy to TEE in visualization of LAA from multiple positions (RA,CS,PA,RVOT and esophagus ). This will be evaluated during the component I of the study.

Hypothesis 2: That ICE can identify low risk patients, CHADS Score < 2,0 in whom immediate cardioversion during the procedure is as safe as based on conventional strategy.

Inclusion Criteria:

1. Patients with paroxysmal/persistent AF
2. Patients with or without structural Heart Disease.
3. Men or Women aged 18 years or older.
4. Patients undergoing an invasive catheterization procedure including right heart catheterization.
5. Patients who give an informed consent for participation in the study.
6. Patients who have undergone a trans-esophageal echocardiogram within the last 48 hours. Patient witch CHADS2 score > 2

Exclusion Criteria:

1. Patients in whom placement of an ICE catheter for adequate atrial visualization is technically not feasible (Right atrium or Esophagus).
2. Women of child bearing potential, in whom pregnancy cannot be excluded.
3. Patients with any medical condition or social circumstance, which in the opinion of the investigator, would make the patient's successful completion of the study doubtful