Instruct: Classify Amazon reviews into positive or negative sentiment
Query: ouch! I didn't hear my heartbeat and my ears hurt!

Not even close to professional quality like advertised. I could barely hear my heartbeat and my son decided I must not be alive when he tried. Since it didn't work well, he lost interest immediately. It also really hurts your ears. I would recommend buying a better quality one at a drugstore for your child to experiment with instead. That's what I'm going to do after I return this one.