DD: intercostal chondritis, strained intercostal muscles
regarding cardiac event: very small likelihood. with no significant health history, young age and athletic background, there is no reason for a cardiac event, especially if you verified a regular rhythm at the time of event. assuming this is not your first workout, you probably stress your heart on a regular basis, which acts as a crude stress test for your heart.
in response to the person saying he had to get shocked...i don't know what your timeline was, but if you had svt/vtach/vfib you would have had other problems before you made it to the doctors office. if it was afib, no dr is going to shock you after a prolong time due to the high risk of release a clot s/p electrocardioversion.