What causes a high pulse rate in young adults?

Hello doctor,

I am a 23-year-old male who is fit and active. I do not drink alcohol or take drugs. I smoke about 15 cigarettes a day and drink some coffee and tea, about two or three cups a day. I do not like energy drinks, so I never take them. I am not on any medication.

About three weeks ago, I started a new job. As one of the requirements of the job is to get a medical test done, I failed it as my heart rate was 140 bpm at rest. My doctor checked it thrice to ensure it was right. He checked my heart rate again over the next week and looked at my blood test results, too. The lowest my heart went was 85 bpm, but mostly it stayed at 100 to 95 bpm. He said he could hear a heart murmur. I did not have this previously.

I do not know if this is related, but I was told I sometimes wake up at night gasping for air, in a sudden manner. I do not have any nightmares as far as I can remember. Other than that, I feel sick often. I do get stomach cramps about two to three times a week.

My doctor sent a letter to the hospital for more tests. He does not know the reason for the high heart rate. I might have to wait for a long time to get the tests done. Is there anything I could do while I wait? Also, my father had a heart attack when he was 45. Could this be a sign that a heart attack is waiting in later years? Should I even be worried, or is this just a normal routine check?

Please help.

Thank you.