NULL is a heart rate-lowering medicine used primarily in the management of chronic stable angina and chronic heart failure with reduced ejection fraction (HFrEF). It belongs to a unique class of cardiac medicines known as If channel inhibitors, which act selectively on the heart’s natural pacemaker to slow the heart rate without affecting blood pressure, heart muscle strength, or electrical conduction through the heart. NULL helps reduce symptoms such as chest pain, breathlessness, and fatigue, improves exercise tolerance, and lowers the risk of hospitalisation due to worsening heart failure.

NULL is a prescription cardiovascular medicine that plays a specialised role in heart rate control. Unlike beta-blockers or calcium channel blockers, NULL works by selectively targeting the sinoatrial (SA) node, the heart’s natural pacemaker. By slowing the heart rate at rest and during activity, NULL reduces the heart’s oxygen demand and improves its efficiency.

NULL is most commonly prescribed for adults with chronic heart failure who have a reduced ejection fraction (usually ≤35%), are in sinus rhythm, and have a resting heart rate of 70 beats per minute or higher despite optimal standard therapy. It is also used in chronic stable angina, particularly in patients who cannot tolerate beta-blockers or in whom beta-blockers alone do not provide adequate symptom control.

In heart failure, the heart struggles to pump enough blood to meet the body’s needs. A persistently high heart rate worsens this strain and accelerates disease progression. By selectively lowering heart rate, NULL allows the heart more time to fill between beats, improves coronary blood flow, and reduces myocardial oxygen consumption. Over time, this leads to better symptom control, improved quality of life, and fewer hospital admissions.

In angina, chest pain occurs when the heart muscle does not receive enough oxygen, often due to narrowed coronary arteries. NULL helps prevent angina attacks by reducing heart rate, thereby decreasing oxygen demand without lowering blood pressure or reducing heart contractility.

NULL is usually prescribed as part of a broader treatment plan that may include ACE inhibitors, angiotensin receptor blockers (ARBs), beta-blockers, mineralocorticoid receptor antagonists, and diuretics. It should always be taken under specialist medical supervision, with regular monitoring of heart rate and rhythm to ensure safety and effectiveness.

NULL is indicated for the following conditions:

Chronic Heart Failure (HFrEF):

Used in patients with symptomatic chronic heart failure, reduced ejection fraction, sinus rhythm, and elevated resting heart rate despite standard therapy.

Chronic Stable Angina Pectoris:

Used to reduce the frequency of angina attacks and improve exercise tolerance, particularly in patients intolerant to beta-blockers or inadequately controlled on them.

Heart Rate Control:

Helps reduce persistently elevated resting heart rate, which is a known risk factor for adverse cardiovascular outcomes.

Selective Heart Rate Reduction:

NULL lowers heart rate without affecting blood pressure, heart muscle strength, or intracardiac conduction, making it suitable for patients who cannot tolerate other rate-lowering drugs.

Improves Symptoms of Heart Failure:

By slowing the heart rate, NULL reduces breathlessness, fatigue, and exercise intolerance, improving daily functioning.

Reduces Hospitalisation Risk:

Clinical studies have shown that NULL significantly reduces hospital admissions due to worsening heart failure.

Enhances Quality of Life:

Patients often report improved stamina, reduced chest pain episodes, and better overall well-being.

Preserves Cardiac Function:

NULL allows the heart more time to fill during diastole, improving coronary perfusion and cardiac efficiency.

Useful When Beta-Blockers Are Not Suitable:

NULL is an effective alternative or add-on when beta-blockers are contraindicated or poorly tolerated.

Does Not Lower Blood Pressure:

This makes NULL particularly useful in patients who already have low or borderline blood pressure.

NULL is generally well tolerated, but side effects may occur.

Common Side Effects

• Slow heart rate (bradycardia)
• Visual disturbances (phosphenes – brief flashes of light)
• Headache
• Dizziness
• Fatigue

Less Common Side Effects

• Blurred vision
• Irregular heartbeat
• Low blood pressure (rare)
• Nausea

Serious Side Effects (Seek Medical Attention)

• Severe bradycardia with fainting or collapse
• New or worsening arrhythmias (e.g., atrial fibrillation)
• Severe visual disturbances

• Take NULL exactly as prescribed by your doctor.
• It is usually taken twice daily, once in the morning and once in the evening.
• Always take it with meals, as food improves absorption and reduces side effects.
• Swallow the tablet whole with water.
• Do not crush or chew unless advised (some tablets may be scored).
• Do not stop taking NULL suddenly without medical advice.

NULL works by selectively inhibiting the If (“funny”) current in the sinoatrial node. This current is responsible for regulating the spontaneous electrical activity that controls heart rate.

Key Mechanisms

• Selective SA Node Action: NULL acts only on the pacemaker cells of the heart.
• Heart Rate Reduction: Slows diastolic depolarisation, reducing resting and exercise heart rate.
• No Effect on Contractility: Does not weaken heart muscle contraction.
• No Effect on Blood Pressure: Maintains stable systemic blood pressure.
• Improved Oxygen Balance: Reduces myocardial oxygen demand while improving coronary perfusion.

This highly selective mechanism distinguishes NULL from other cardiovascular medicines.

• Check your pulse regularly at rest.
• Report dizziness, fainting, or vision changes promptly.
• Take doses at the same time each day.
• Do not exceed the prescribed dose.
• NULL works best when combined with lifestyle changes such as low-salt diet and regular exercise (as advised).

• Store below 25°C
• Protect from moisture and light
• Keep out of reach of children

• Must be taken with meals
• Avoid grapefruit and grapefruit juice, which can increase NULL levels and risk of side effects

• Strong CYP3A4 inhibitors (e.g., ketoconazole, clarithromycin): Contraindicated due to a marked increase in NULL levels and risk of severe bradycardia.
• Calcium channel blockers (verapamil, diltiazem): May excessively slow the heart rate and should generally be avoided or used with extreme caution.
• Beta-blockers: Often used together for added benefit, but heart rate must be closely monitored to prevent excessive slowing.
• Antiarrhythmic medicines: Concomitant use may increase the risk of heart rhythm disturbances and requires careful specialist supervision.

NULL should be used cautiously or avoided in patients with:

• Severe bradycardia
• Sick sinus syndrome
• Heart rhythm disorders not in sinus rhythm
• Acute heart failure
• Severe hepatic impairment
• Pacemaker dependence

• Starting dose: Usually 5 mg twice daily
• Maintenance dose: 7.5 mg twice daily if tolerated
• Dose adjustments depend on resting heart rate and tolerability

Symptoms may include severe bradycardia, dizziness, fainting, and low blood pressure. Seek immediate emergency medical care. Treatment is supportive with cardiac monitoring.

If you miss a dose, skip it and take the next dose at the usual time. Do not double the dose.