What you are feeling could be an extra heart beat, also called as an ectopic beat
or an extra-systole. If it is happening frequently, it can be recorded by an ECG. If it happens only a few times a day, it needs a 24 hour Holter monitor
to record it. At your age and with the long history of smoking, you need a complete cardiac evaluation including tests for BP, sugar, cholesterol
, kidney function, hemoglobin
, ECG, echo, chest x-ray and a treadmill test. There is still time to take preventive steps to avert major catastrophes....so, dont worry.