What was Willem Einthoven's significant contribution to medicine?

Willem Einthoven's significant contribution to medicine was the invention of the first practical electrocardiogram (EKG or ECG). This groundbreaking development allowed for a non-invasive method to measure the electrical activity of the heart, providing vital information that could be used to diagnose various cardiac conditions. Einthoven's work laid the foundation for modern cardiology, enabling healthcare providers to better understand heart function, detect abnormalities, and monitor cardiac health.

The EKG was a major advancement in medical technology, as it transitioned from theoretical concepts of electrical heart activity to a practical application that could be utilized in clinical settings. Einthoven was awarded the Nobel Prize in Physiology or Medicine in 1924 for his innovative work, which has significantly impacted patient care and the understanding of cardiac health.

In contrast, the other contributions mentioned do not relate to Einthoven. Penicillin was discovered by Alexander Fleming, the stethoscope was developed by René Laennec, and modern surgical techniques evolved through the contributions of various individuals over time.