What does a 48 hour hoelter monitor show.. does it show congestive heart failuer?

No, holter monitoring only records heart rhythm for detecting cardiac arrhythmia, not the heart pump (EF) which is the main indicator of congestive heart failure (CHF). However, cardiac arrhythmia such as premature ventricular contractions or paroxysmal atrial fibrillation or non sustained ventricular arrhythmia can be present is CHF so the presence of arrhythmia can be an indirect sign of CHF.

Holter monitoring is typically used to diagnose paroxysmal arrhythmias that may be involved in rapid CHF decompensations that result usually in frequent hospital stays, otherwise not typically used in patients with CHF, nor diagnostic of CHF.