By Antibodies and Plasma cells
I would think more relaxed would be the best option since exercise can help with stress.
Its a symptom of any number of things; Pericardial Tamponades (fluid buildup of sac surrounding heart), a heart contusion, a dysrhytmia like Ventricular Fibrillation or Ventricular Tachycardia...
The answer to your question, is D
hope this helps :D