<s>[INST] Hi Dr Samuel,My Girlfriends heart is beating really hard and every time it beats hard, it makes her really tired. What may be the cause? She has no record of any heart diseases, but she have had really little hours of sleep recently.Thank you.Best RegardsKoo [/INST] Hello. Thank you for your question and welcome to Chat Doctor. I understand your concern. Well, if this hard heart beat is also associated sometimes with a shortness of breath, combining with the lack of sleep and/or with the usage of energetic Chat Doctor.  In young ages and when they are not usual phenomenons within a day, there is nothing to worry about. Stressful moments in life, physical or psychological, can be associated with extrasystoles. If this is a worrisome event to her and to you, I recommend her to be put on a 24-hour Holder rhythm monitor, to determine exactly what are these phenomenons, and if they are present, are there enough episodes a day to warrant treatment (because there is a cut-off line in the number of extrasystoles that can be tolerated). Instead, there is the option of the episode rhythm monitor - a machine who can be turned on and off by user, when he/she experiences the symptom. When the readings are ready, I suggest you to consult a cardiologist or feel free to ask me again. I hope I was helpful. Take care. Best regards,  </s>