The chronotropic effect is caused by stimulation of the nervous system and causes the heart rate to

The sympathetic nervous system is stimulated and leads to chronotropic effects. This leads to an increase in heart rate. The sympathetic and parasympathetic nervous systems are complementary parts of the autonomic system, which works at a baseline level at all times, taking care of the body's unconscious, baseline activities.

The balloon will expand or explode (with enough time)

Explanation:

Charles law states that the volume of a fixed gas is directly proportional to the temperature and pressure. The higher the temperature, the higher the pressure. This will raise the volume, causing the balloon to expand at the very least.