Among the initial 492 patients who underwent balloon aortic valvuloplasty as part of the Mansfield Investigational Device Exemption Protocol, 31 (6.3%) had acute catastrophic complications. These included ventricular perforation in nine (1.8%), seven women and two men; six cases (67%) involved serial balloon inflations and seven (78%) also involved dual balloon inflations. In six (67%) of the nine patients perforation was fatal. In four patients studied at necropsy, the perforation involved the base of the lateral left ventricular free wall. Pericardioentesis was performed in five patients, three of whom survived with (one patient) or without (two patients) operative repair. Acute, severe aortic regurgitation developed in four patients (0.8%), all women. None had significant regurgitation before valvuloplasty; dual balloons were used in two of the four. All three patients who underwent emergency valve replacement survived. A fourth patient died 2 days after valvuloplasty without operative intervention. Fatal cardiac arrest complicated balloon aortic valvuloplasty in 13 patients (2.6%), including 7 with cardiogenic shock and 4 with refractory ventricular arrhythmias. Of the seven with shock, four had been treated with serial balloon inflations; dual balloons were used in three. In two of three patients studied at necropsy, the aortic valve was observed to be congenitally bicuspid. A fatal cerebrovascular accident occurred in two patients (0.4%); it was hemorrhagic in one, embolic in another. Both patients were treated with serial (including one dual) balloon inflations. Limb amputation was required in three patients (0.6%), two women and one man; in two patients amputation was above the knee, in the third patient it was limited to two toes. In all, catastrophic complications of balloon aortic valvuloplasty were ultimately fatal in 24 (77%) of the 31 patients.