Having a fast resting pulse rate, even if you are physically fit, increases death risk, according to a study.
Researchers found men with a "high end of normal" resting heart rate of 90 beats per minute had treble the death risk of others with much slower pulses.
The investigation, in the journal Heart, looked at nearly 3,000 middle-aged men from Denmark over a period of 16 years.
Experts say much more work is needed to confirm and understand the link.
They say it is difficult to draw firm conclusions because the study authors did not track the men's fitness - instead they relied on medical records taken years before the research began.
Arguably, the men's fitness could have deteriorated since and this could have influenced the study results.
Nonetheless, the study authors believe their work suggests that a fast resting pulse - taken when having been inactive for at least five minutes - is a risk factor in its own right, regardless of general physical fitness.
And the higher the resting heart rate, the higher the risk of death.
Doctors already know that having an abnormally high resting heart rate - 100 bpm or more - can be risky and increases the likelihood of problems such as heart attack and stroke.
A fast resting heart rate also tends to go hand in hand with other cardiovascular risk factors, such as higher blood pressure and smoking.
In the study, the researchers tried to control for this.
As might be expected, men with slower heart rates tended to be fitter while many of those with higher resting heart rates were less physically fit and had other heart risk factors like high blood pressure.
After adjusting for this, the link between higher heart rates and increased death risk persisted.
Doireann Maddock of the British Heart Foundation said: "Despite this research, we don't yet know for sure if an elevated resting heart rate is an independent risk factor for mortality.
"The research had its limitations because it only looked at healthy, middle-aged and elderly Caucasian men and so the findings may not necessarily apply to the general population in the UK.
"Rather than worrying about these findings, you'd be better off focusing on stopping smoking, maintaining healthy blood pressure and cholesterol levels, keeping active and watching your weight.
"Anyone aged 40 or over should also contact their GP surgery for an NHS Health Check, which fully assesses your risk of heart disease and then helps you stay heart healthy."