Hypertrophic pyloric stenosis is a condition in infants where the pyloric muscle thickens, causing projectile vomiting. It is usually diagnosed between 4-8 weeks of age when vomiting becomes frequent and forceful. On physical exam, doctors may feel an olive-sized pyloric tumor. Ultrasound confirms the diagnosis by showing thickened pyloric muscles. The standard treatment is Ramstedt pyloromyotomy surgery to cut the thickened pyloric muscle. After resuscitation from dehydration, the surgery cures the condition and babies can resume feedings within a day.