Your question implies that the setting of the story takes place in the 1960 s. If that is the case you have a historic problem with a patient recovering from a cardiac bypass surgery. From 1960 to 1967, several sporadic instances of coronary grafting were reported. All were isolated cases and, for uncertain reasons, were not reproduced. http://cardiacsurgery.ctsnetbooks.org/cgi/content/full/2/2003/3ck=nck#THE_DEVELOPMENT_OF_CARDIOPULMONARY_BYPASS So cardiac bypasses did not become a relatively routine procedure until the mid to late 1970 s. One relatively common complication associated with post bypass surgery is a ventricular arrhythmia. Any medication that is pro-arrhythmic could help precipitate the problem - for which a post bypass patient is at risk for any way. Again in 1960 s perspective. *Tricyclic antidepressants such as amitriptyline *Too little potassium usually from too much diuretic such as Lasix without potassium replacement. *Antibiotics such as Erythromycin *Antipsychotics such as Thioridazine. Any combination of the above would theoretically have expotential effects when added together. All of the medications I named were around and were used in the 1960 s. In those days, I am relatively sure that they did not have external pacemakers, either. I hope this helps. Good luck.