I am 79 years old male and noticed that my pulse rate in the night during sleep is within 50-55 bpm: and during day time is 55-60 bpm while at rest inhone . Whenever I go for walking either in morning or evening the pulse rate increases slowly up to 105 bpm. I have checked through ecg, echo and coronary citi angiography and doctor found no abnormality. Besides I have no diabetes or high cholesterol. The BP is also within limit by taking medicines. The X-ray chest and usg of abdomen have no abnormalities. I am unable to address the issue by doctors even changing BP medications. Please advise the best course of action