Background: Protection and preservation of fetal myocardial function are important for successful fetal intracardiac repair. Our objective was to determine fetal biventricular cardiac performance after two cardiac-arrest techniques. Methods: Three groups of midterm ovine fetuses underwent 90-minute bypass. A control group (no arrest shams, n = 3), and two groups that included 20 minutes of arrest, using fibrillatory (n = 3) or blood cardioplegia (n = 3), were compared. Blood cardioplegia consisted of 4:1 cold blood to crystalloid solution induction every 10 minutes, followed by a warm shot terminal dose before clamp removal. Myocardial function variables from biventricular intracardiac pressure catheters, and 3-axes cardiac sonomicrometry, fetal hemodynamics, and arterial blood gases were continuously recorded. Fetal myocardium was collected for troponin-I analysis at 90 minutes. Statistical analysis was by two-way analysis of variance for repeated measures. Results: Compared with sham, right ventricular myocardial contractility was reduced with plegia but not fibrillation at 90 minutes after arrest: dP/dt max (511 ± 347 vs 1208 ± 239, p < 0.01) and preload-recruitable stroke work (7.2 ± 8.5 vs 32.3 ± 14.6, p < 0.01). Right ventricular end diastolic pressure-volume relationship (ventricular stiffness) worsened by 90 minutes for plegia vs fibrillation (0.84 ± 0.18 vs 0.25 ± 0.16, p < 0.05). There were no differences in left ventricle performance between groups. Fetal heart rate increased in shams by 30 minutes after arrest compared with both arrest groups (p < 0.05). Right ventricular troponin-I degradation increased with plegia, but not fibrillation, compared with sham (p < 0.05). Conclusions: In vivo, fetal right ventricular contractile function deteriorates with a common blood-plegia regimen. Fibrillatory arrest better preserves right ventricular function, the dominant ventricle in fetal life, for short arrest periods.