Leo Morimoto’s “Sudden Death of Unknown Cause”… A Doctor Warns of “5 Life-Threatening Diseases and Warning Signs You Must Not Overlook”

“We were talking normally just yesterday.” “He went to sleep just as usual.”—

And yet, life can be taken away suddenly.

Leo Morimoto, who had been active for many years as an actor and narrator, passed away on September 4 at the age of 83. According to his agency, it was a “sudden death of unknown cause.”

Morimoto is best known for appearing in numerous acclaimed dramas such as *Shomuni* and *Long Vacation* (both on Fuji TV). He was also beloved by people of all ages as a narrator for anime series like *Thomas & Friends*, where he made full use of his beautiful voice.

The news of Mr. Morimoto’s sudden passing is shocking. While there are cases like this one where the cause cannot be determined, in Japan, approximately 91,000 people suffer sudden cardiac arrest each year (according to the Ministry of Internal Affairs and Communications’ Fire and Disaster Management Agency’s “Reiwa 7 Edition: Current Status of Emergency Medical Services and Rescue Operations”).A simple calculation shows that approximately 250 people die each day from sudden cardiac death.

When we hear the term “sudden death,” we tend to imagine a life being taken without any warning, but there are also cases where the body sends out subtle SOS signals.

“My chest feels a little heavy.”
“I’ve been getting short of breath easily lately”
“My vision went dark for a moment”
“I had a headache unlike any I’ve ever experienced before”

Brushing off these symptoms as “just being tired” or “just part of aging” can sometimes delay the detection of a serious illness. What kinds of illnesses can lead to sudden death? What are the warning signs you must not overlook?

We asked Dr. Yoshimasa Goto, Chairman of the Board of Directors of the Gorokai Medical Corporation (quotes below are from Dr. Goto).

“Sudden death” is not a medical diagnosis

First and foremost, it’s important to understand that “sudden death” is not a medical diagnosis in itself.

“Sudden death is a term that refers to an unexpected death occurring suddenly; it is not a medical diagnosis. Serious illnesses affecting the heart, blood vessels, or brain may be underlying the condition. In Mr. Morimoto’s case, his agency has announced that the cause is ‘unknown,’ so it is impossible to speculate on the cause of death from the outside.

Generally speaking, it is possible for someone who appeared to be living a normal life just yesterday to suddenly lose their life due to a rapid deterioration of a heart or vascular disease. That is what makes sudden death so frightening.”

The Tokyo Metropolitan Institute of Forensic Medicine defines sudden death as “instantaneous death or death occurring within 24 hours of the onset of acute symptoms, excluding deaths due to external causes.” According to the institute, “acute cardiac death” is the most common type of sudden death, and the vast majority of these cases are due to ischemic heart disease.

There are five major diseases that can lead to sudden death.

① Acute myocardial infarction—it doesn’t always involve “severe chest pain”

The first condition to be aware of is “acute myocardial infarction.” This is a condition in which the coronary arteries—which supply oxygen and nutrients to the heart—become blocked, cutting off blood flow to the heart muscle.

“Typical symptoms include severe, constricting chest pain or a feeling of pressure. However, a heart attack does not necessarily mean you will experience severe chest pain. You may feel heaviness in the chest, shortness of breath, cold sweats, or nausea. You may also experience discomfort in your shoulders, arms, back, jaw, or upper abdomen.

“Particularly among the elderly and those with diabetes, there is a type known as a ‘painless myocardial infarction’ where little or no pain is felt, and symptoms may not be typical. It is dangerous to make a self-diagnosis based on the assumption that ‘since my chest doesn’t hurt, it can’t be my heart.’”

Mr. Morimoto suffered a heart attack in 2010 at the age of 67 and was transported to the hospital by ambulance. According to news reports at the time, he complained of pain from his chest to his upper abdomen while at home and contacted his manager himself. He was transported by ambulance and diagnosed with a heart attack.

However, the causal relationship between his previous heart attack and this sudden death has not been established. Dr. Goto points out the following as a general principle:

“The danger of a heart attack isn’t limited to damage to the heart muscle. It can trigger dangerous arrhythmias, such as ventricular fibrillation, which can lead to sudden cardiac arrest. If you experience persistent chest discomfort, cold sweats, shortness of breath, or any symptoms that are clearly different from usual, don’t try to tough it out—go to the hospital immediately.”

② Lethal Arrhythmias—“Losing Consciousness for a Moment” Is Also an Important Sign

The second type is “life-threatening arrhythmias,” such as ventricular fibrillation and ventricular tachycardia. The heart contracts rhythmically in response to electrical signals, pumping blood throughout the body. When these electrical signals become severely disrupted, the heart can no longer pump blood normally.

“In the case of ventricular fibrillation in particular, the heart muscle simply quivers rapidly and can no longer function adequately as a pump. Since blood can no longer reach the brain, you will lose consciousness within a short time, leading to cardiac arrest. Prompt cardiopulmonary resuscitation (CPR) or treatment with an automated external defibrillator (AED) is necessary.”

What makes this condition so frightening is that it “occurs suddenly,” though some people do experience warning signs before an episode.

“Be alert to symptoms such as unusually strong palpitations, shortness of breath, dizziness, a sensation of darkness before your eyes, or fainting—especially if these are new to you. It’s dangerous to think, ‘I lost consciousness for a moment, but I came to right away, so I’m fine.’ This is because severe arrhythmia may be lurking behind the fainting episode.”

The Japanese Circulation Society also notes that ventricular fibrillation and ventricular tachycardia can occur in the context of conditions such as myocardial infarction or cardiomyopathy, and urges people to consult a doctor if they experience previously uncharacteristic symptoms such as palpitations, shortness of breath, fainting, or dizziness.

③ Acute Aortic Dissection—Sudden “Intense Pain in the Chest or Back”

The third condition is “acute aortic dissection.” The aorta is the body’s largest blood vessel, through which blood first flows after being pumped from the heart. This condition occurs when the wall of the aorta suddenly tears, allowing blood to seep into the space between the layers of the vessel wall.

“The typical symptom is ‘sudden, extremely severe pain in the chest or back.’ Patients often describe it as ‘pain unlike anything I’ve ever experienced before’ or ‘a sudden, tearing pain in my chest or back.’ As the dissection progresses, the location of the pain may shift from the chest to the back and even to the lower back.”

Symptoms are not limited to the chest and back.

“If blood flow to the brain is impaired, it can lead to impaired consciousness or paralysis of the limbs. If the condition affects the blood vessels of the heart, it can result in a condition similar to a heart attack.

If the aorta ruptures or if ‘cardiac tamponade’ occurs—where blood accumulates within the membrane surrounding the heart (the pericardium), preventing the heart from functioning properly—it can lead to sudden death. High blood pressure is a major risk factor for aortic dissection. Aortic dissection is a life-threatening emergency. Do not ignore sudden, severe chest or back pain, thinking, ‘It will probably go away if I rest for a bit.’”

④ Pulmonary Thromboembolism—Be Alert to “Sudden Shortness of Breath”

The fourth condition is “pulmonary thromboembolism.” A blood clot formed in a vein—such as in the leg—travels through the bloodstream to the lungs, where it blocks a pulmonary artery. When this occurs due to remaining in the same position for a long time, it is called “economy class syndrome.”

“Characteristic symptoms include sudden shortness of breath and chest pain. In severe cases, the lungs cannot receive an adequate blood supply, leading to a drop in blood pressure, which can result in loss of consciousness or cardiac arrest.”

Caution is necessary for individuals in situations where blood clots are more likely to form, such as after surgery, during prolonged bed rest, or in patients with cancer.

In some cases, symptoms may first appear in the legs before affecting the lungs.

“One leg may suddenly swell or become painful. If you then experience sudden shortness of breath or chest pain, you should suspect pulmonary thromboembolism.”

⑤ Subarachnoid Hemorrhage — “A Headache Like You’ve Never Experienced Before”

Brain disorders can sometimes lead to sudden death. A prime example is “subarachnoid hemorrhage.” An aneurysm or other abnormality in a blood vessel in the brain ruptures, causing bleeding into the subarachnoid space—the area beneath the arachnoid membrane, one of the three layers covering the brain.

“A very important sign is a sudden, severe headache. It is often described as ‘a headache unlike any you’ve ever experienced before.’ It may be accompanied by nausea or vomiting, and in severe cases, the person may lose consciousness on the spot. Sometimes, a relatively mild headache—known as a ‘warning headache’—occurs before the full-blown bleeding begins.”

People who suffer from headaches need to be on guard.

“People tend to think, ‘It’s probably just my usual headache,’ but is it really the same as your usual headache? If the headache is clearly different from usual, it’s important to seek medical attention immediately rather than just taking pain relievers and waiting to see what happens.”

Don’t Brush It Off as “Just a Sign of Aging”

What should you watch out for in your daily life? Dr. Goto advises against making judgments based solely on “the intensity of the pain.”

“Just because a condition can lead to sudden death doesn’t mean it will present with severe symptoms right from the start. Especially as we get older, we tend to think, ‘I’ve been getting tired easily lately because I’m getting older,’ or ‘My shortness of breath is just part of aging.’

If you experience ‘changes that are different from how you used to be’—such as suddenly getting short of breath over a distance you used to walk without trouble, feeling an unfamiliar discomfort in your chest, or experiencing repeated palpitations—I want you to stop and think about it.”

He notes that immediate medical attention is required for sudden, severe chest pain or a feeling of chest tightness; sudden, severe shortness of breath; fainting; sudden, severe headaches; loss of consciousness; or paralysis on one side of the body.

“It’s dangerous to think, ‘I’ll wait until morning’ or ‘It’ll go away if I get some sleep.’ With conditions such as a heart attack, aortic dissection, or subarachnoid hemorrhage, the time until treatment begins is critically important. If you’re unsure whether to call an ambulance, please consult your local emergency hotline (such as #7119).”

It’s also important to notice when someone around you is acting unusual.

“If someone collapses right in front of you, is unresponsive, and isn’t breathing normally, call 119 immediately and do not hesitate to perform chest compressions and use an AED. The actions of bystanders can save a life.”

Just because someone was fine yesterday doesn’t mean they’ll be okay today. That said, there’s no need to live in constant fear of every physical change. Dr. Goto concludes by saying:

“Not all sudden deaths have warning signs. There are cases where it happens truly out of the blue and is difficult to predict. Therefore, it’s incorrect to think that ‘sudden death can be prevented if you just know the warning signs.’ What’s important is not to take ‘unusual’ changes in your body lightly.

Don’t assume it’s ‘just fatigue,’ ‘just part of getting older,’ or ‘it’ll go away after a good night’s sleep.’ If concerning symptoms persist, see a doctor. If you suddenly experience severe symptoms, don’t hesitate to call 911. That’s what saves lives.”

“I was fine yesterday, so I’ll be fine today.”

There are illnesses where that common-sense assumption doesn’t hold true. Sudden chest pain, shortness of breath, fainting, or an intense headache unlike anything you’ve ever experienced—

Not overlooking the “unusual” SOS signals your body sends is the first step in protecting your own life and the lives of those close to you.