I had a heart murmer that was considered benign after echo ever since murmer i have had a hign resting heart rate of 155+ what could cause the hr?

Tachycardia: The normal heart rate (hr) for most patients is 60-100bpm. A resting hr of 155+ is very abnormal and dangerous, especially if persistent. It is usually the sign of either an electrical conduction problem with the heart or chronic use of stimulants - ie, decongestants, cocaine, caffeine. An echo would not identify causes of a rapid hr. I doubt ur dr would have ignored such a high hr. See dr asap