Answer
The answer is Leiden, a city in the Netherlands. Einthoven, the renowned physiologist and Nobel laureate, passed away in Leiden on September 29, 1927. He is remembered for his groundbreaking research on the electrical activity of the heart, leading to the development of the electrocardiogram (ECG). Einthoven's contributions revolutionized the field of cardiology and continue to have a profound impact on the diagnosis and management of heart conditions.