The next time you try the same feat, you will probably find that you can go a little farther, or faster, without making it throb.

Indeed, getting into training is very largely getting the heart built up and educated, so that you can run or play, or wrestle hard without overtaxing it.

Whatever you can do within the limits of your heart is safe, wholesome, and invigorating; whatever goes beyond this, is dangerous and likely to be injurious.
[Illustration: ROWING IS A SPLENDID EXERCISE FOR HEART AND LUNGS] Occasionally, however, some of the nerves which control the heart become disturbed or diseased so that, instead of the heart's simply beating harder and faster whenever more blood is really needed, it either throbs and beats a great deal harder and faster than is necessary, or goes racing away on its own account, and beats "for dear life," when there is no occasion for it, thus tiring itself out without doing any good, and producing a very unpleasant feeling of nervousness and discomfort.

This may be due to overwork, whether with muscles or brain; or to worry or loss of sleep, in which case it means that you must put on the brakes, take plenty of rest and exercise in the open air, and get plenty of sleep.

Then these danger signals, having accomplished their warning purpose, will disappear.
Other Causes of Heart Trouble.