We present a brief summary of the 10 greatest cardiologic developments and discoveries of the 20th century Described are electrocardiography; preventive cardiology and the Framingham Study; "lipid hypotheses" and atherosclerosis; coronary care units; echocardiography; thrombolytic therapy; cardiac catheterization and coronary angiography; open-heart surgery; automatic implantable cardiac defibrillators; and coronary angioplasty. These topics are the personal choices of the authors.