What is a notable negative effect of using non-dihydropyridine calcium channel blockers in heart failure patients?

The correct choice highlights a significant concern when using non-dihydropyridine calcium channel blockers in heart failure patients, which is their negative inotropic effect. This means that these medications decrease the force of cardiac muscle contraction. In heart failure, especially with reduced ejection fraction, the heart's ability to pump effectively is already compromised. Using agents that further weaken cardiac contractility can lead to worsening heart failure symptoms and potential exacerbation of the condition.

In contrast, the other options represent effects that are not directly associated with the primary concern of using non-dihydropyridine calcium channel blockers in this patient population. For instance, increased heart rate is typically more characteristic of dihydropyridine calcium channel blockers, which primarily act on vascular smooth muscle rather than the heart itself. Renal failure may occur due to various factors in heart failure but is not an inherent effect of the non-dihydropyridine class. Gastrointestinal disturbances can occur with a wide range of medications but are not specifically notable concerns associated with the use of these calcium channel blockers in heart failure treatment.