Hello! Welcome and thank you for asking on HCM! I understand your concern and would explain that his symptoms seem to be related to a cardiac arrhythmia. What is his age? What about his past medical history? What are his blood pressure values? Has he had any fevers during these days? The painful lump on his chest may be an infection or a lymph node. The facts that it hurts, means that it is inflammatory. I recommend consulting with the GP for a careful physical examination (including the inspection of the lump), a resting ECG, a chest x ray and some blood lab tests: - complete blood count - PCR, sedimentation rate (inflammation tests) - kidney and liver function tests - fasting glucose - thyroid hormone levels (thyroid gland function) - cortisol plasma levels (adrenal gland function) - blood electrolytes, etc. A 24-48 hours ECG monitoring is necessary to rule in/out a possible cardiac arrhythmia. A biopsy of the lump on his chest may be needed to determine its nature (infectious, inflammatory, etc). A 24 hours urinary metanephrines test for possible pheochromocytoma should be performed if his episodes of tachycardia are associated with high blood pressure and other symptoms (pale skin, sweating, etc). Hope to have been helpful! Feel free to ask any other questions, whenever you need! Best regards, Dr. Iliri