Which of the following is a cardiovascular risk of ephedra?

Myocardial infarction, commonly known as a heart attack, is a significant cardiovascular risk associated with the use of ephedra. Ephedra contains alkaloids that can stimulate the nervous system and increase heart rate and blood pressure, potentially leading to serious cardiovascular events. The overstimulation of the heart can contribute to the development of arrhythmias, which might escalate to myocardial infarction, especially in individuals with pre-existing heart conditions or those who consume higher doses. Understanding this risk is particularly crucial as it highlights the importance of caution when considering stimulants like ephedra, especially for those with cardiovascular issues or risk factors.

The other options do not specifically relate to the direct cardiovascular risks posed by ephedra. While diabetes can be influenced by various factors and cholesterol levels can also be affected by multiple lifestyle choices, they are not direct consequences of ephedra use. Insomnia is a common side effect due to the stimulating nature of ephedra but doesn't constitute a cardiovascular risk in the same manner as myocardial infarction. This distinction is vital for effective understanding of the risks linked to ephedra in the context of cardiovascular health.