Valvuloplasty for mitral stenosis. Harken reported the first successful intracardiac operation for treatment of this lesion--a procedure was first attempted in the 1920s. Charles Bailey in Philadelphia undertook a similar approach at the same time, and according to Lawrence Cohn "These surgeons began the 'modern' era of cardiac surgery." (L. H. Cohn, "Surgical Treatment of Valvular Heart Disease," Am. J. Surg. 135, 444-451, 1978). With L. B. Ellis, P. F. Ware. 

"In 1959 Bernard Lown commenced research in his animal laboratory in collaboration with engineer Barouh Berkovits into a technique which involved charging of a bank of capacitors to approximately 1000 volts with an energy content of 100-200 joules then delivering the charge through an inductance such as to produce a heavily damped sinusoidal wave of finite duration (~5 milliseconds) to the heart by way of paddle electrodes. This team further developed an understanding of the optimal timing of shock delivery in the cardiac cycle, enabling the application of the device to arrhythmias such as atrial fibrillation, atrial flutter, and supraventricular tachycardias in the technique known as "cardioversion" (Wikipedia article on Defibrillation, accessed 4-2020).

Harken and colleagues reported "the first clinical use of an implantable noncompetitive pacer" (Jeffrey, Machines in Our Hearts. Baltimore, 2001, 134.) Berkovits, an engineer working for Medtronic, was an inventor of the device.