Health Library Medical Encyclopedia Health Navigator Drug Interactions Drug Notes Health Capsules Smart Sites Back Pain Hip Pain Knee Pain Weight Loss Medical Encyclopedia Take Charge of Your Health Research a disease or condition Lookup a symptom Learn about a test Prepare for a surgery or a procedure Learn what to do after being discharged Get More Out of Your Care Self-Care Instructions Questions to Ask Your Doctor Nutrition, Vitamins & Special Diet Understand An Emergency Injuries Poison Health Library Videos What makes your heart beat? The cardiac conduction system is a group of specialized cardiac muscle cells in the walls of the heart that send signals to the heart muscle causing it to contract. Tips on buying cold and flu medicines. They call it the common cold for a reason. Colds are extraordinarily common. Children average 3 to 8 colds a year and adults almost that many. Cold treatments for kids. When people started saying that you shouldn't use decongestant, antihistamine, or cough suppressants in kids under 6 or maybe even kids under 12, parents started asking me lots of questions.