Implantable heart-monitoring devices, such as defibrillators, pacemakers, and cardioverters, detect onset of abnormal heart rhythms and automatically apply corrective electrical therapy, specifically one or more bursts of electric charge, to abnormally beating hearts. Critical parts in these devices include the capacitors that store and deliver the bursts of electric charge. Some devices use flat aluminum electrolytic capacitors have cases with right-angle corners which leave gaps when placed against the rounded interior surfaces of typical device housings. These gaps and voids not only waste space, but ultimately force patients to endure implantable devices with larger housings than otherwise necessary. Accordingly, the inventors devised several capacitor structures that have curved profiles conforming to the rounded interior surfaces of device housings. Some exemplary capacitor embodiments include two or more staggered capacitor elements, and other embodiments stagger capacitors of different types and/or sizes.