Conversation: The conversation between human and AI assistant.
[|Human|] My daughter is 3 years old, she was complaining of a head ache tonight and was crying for abuot 15 minutes before she fell asleep. I listened to her heart beat while she was sleeping and for the most part it sounded regular, but when she would take a deep breath it sounded like it slowed down, if this normal for a child or should I be worried? I am familiar with heart sounds so I can tell its a little different, but I am used to adult heart beats. Thanks
[|AI|]  Thanks for consulting at Chat Doctor. It is normal and physiological. You need not worry. Heart rate increases while breathing in (inspiration) and decreases while breathing out (expiration). This is to compensate for the decreased left ventricular output while breathing in. During inspiration, more blood gets pooled in the lungs so that left ventricle gets less blood to pump out. By increasing the heart rate with a reflex mechanism, body maintains the cardiac output. In contrast, left ventricular output is higher in expiration and heart rate lower.