Like they mentioned its probably pac or pvc,nothing to worry abt if ur echo is normal.if you got lots of it in a day,then get a 24 hour holter.
Sounds like classic (textbook description) palpitations; PACs or PVCs. Should however be confirmed by a doctor, if you do it will be easier to relax. Get it monitored with EKG and make sure you are stressed when seeing the doctor. A monitoring without having the symptoms is worthless.
You are feeling palpitations of some sort. From what you describe, it "could" be something like PVCs/PACs which are typically benign in a structurally normal heart, but there are certainly heart arrhythmias that do require treatment. The only way to diagnose what you have and whether treatment is required is to see your doctor and capture the events on a monitor.