Calf: The belly or fleshy hind part of the back of the leg below the knee. The calf is made up mainly of the gastrocnemius muscle. Pain in the calf is commonly caused by muscle strain, but can be caused by blood clots in veins of the legs. SLIDESHOW Heart Disease: Causes of a Heart Attack See Slideshow From Healthy Resources 10 Rheumatoid Arthritis SymptomsWhat Is Exocrine Pancreatic Insufficiency?Understanding COVID-19 Testing and Treatment Featured Centers What Are the Best PsA Treatments for You?Understanding Biologics 10 Things People With Depression Wish You Knew Health Solutions From Our Sponsors Shot-Free MS Treatment Your Child and COVID-19