Fruit lovers need to know that everything in fruits is not good to eat. It has been tested that seeds of apples and pits of cherries contain cyanogenic compounds that can cause poisoning. The extent of these compounds is not so much that an adult cannot bear it but children and pets are very much at risk.
Adults can also succumb to the poison if they consume too much of the seeds. Also if they chew it, then it can be more harmful. If swallowed, the immune system can counter the toxicity better. Cyanide is the most feared poison as it can cause death instantly if a certain quantity is taken by living beings including humans. Seeds obviously do not carry that much amount but enough to cause headache, difficulty in breathing, nausea and rise in blood pressure.
Thus you all are strongly recommended to discard the seeds and enjoy the fruits.